In his invitation to Wednesday's Brussels summit to discuss Prime Minister Theresa May's request for a delay to the U.K.'s scheduled Friday departure from the EU, Tusk says "I believe we should also discuss an alternative, longer extension. One possibility would be a flexible extension, which would last only as long as necessary and no longer than one year."
Tusk says such an extension would have to be conditional to allay fears Britain could stymie EU decision making if it remains a member. He says conditions would include not reopening the withdrawal agreement and the U.K. continuing to sincerely cooperate with the bloc.
British Prime Minister Theresa May is meeting French President Emmanuel Macron in Paris to discuss the possibility of a further delay to Brexit.
Macron greeted May in the Elysee presidential palace with a hug. They both smiled for photographers.
The two leaders are not scheduled to make any press statement.
May earlier met with German Chancellor Angela Merkel in Berlin.
The French presidency said all decisions on Brexit will be made on Wednesday at a summit of EU leaders in Brussels.
A delay requires the unanimous support of the EU's other 27 members. If they refuse, Britain faces a sudden departure on Friday.
Talks between the British government and its political opponents have failed to reach a Brexit compromise before the European Union decides whether to grant the U.K. a delay to its departure from the bloc.
But the Conservative government and the Labour Party say they will resume negotiations after Wednesday's EU summit.
Prime Minister Theresa May hopes to persuade the 27 other EU leaders that she has a plan to end Britain's Brexit impasse so that they will agree to postpone Britain's departure, currently scheduled for Friday.
After failing three times to get her Brexit deal through Parliament, May opened negotiations with Labour, which favors a softer version of Brexit.
May's office said talks Tuesday had been "productive and wide-ranging" and both parties appreciated the urgency of finding a solution.
Labour business spokeswoman Rebecca Long-Bailey said there had not been "any fundamental shift ... but we're hopeful that progress will be made."
German news agency dpa reports that Chancellor Angela Merkel has told her party's lawmakers that delaying Britain's exit from the European Union may be possible.
Merkel held an hour of talks with British Prime Minister Theresa May in Berlin on Tuesday, a day before EU leaders are due to decide on London's request for another Brexit extension. The current departure date is April 12, but May has requested a delay to June 30.
The dpa agency quoted unnamed participants at a closed doors meeting of Merkel's Union bloc in parliament saying the chancellor had informed them that a delay until the end of the year or early 2020 would be possible.
Merkel reportedly also told participants that Britain would have to take part in European Parliament elections unless it leaves the bloc by May 22.
Merkel's office declined to comment on the meeting with May.
A top official at the French presidency says France is not ruling out the prospect of backing a further delay to Brexit.
Just ahead of a planned meeting between Prime Minister Theresa May and French President Emmanuel Macron in Paris, the official said the key point for France is to get "solid guarantees" that the U.K.'s prolonged presence would not disrupt the functioning of EU institutions.
The official, who spoke anonymously ahead of sensitive talks in accordance with the French presidency's customary practice, said Macron expects from May to provide a "credible prospect" to avoid a 'no-deal' Brexit on April 12, including the possible outcome from ongoing talks between Britain's government and opposition Labour Party.
EU leaders meet in Brussels on Wednesday. Any extension to the Brexit deadline requires the unanimous support of the 27 other member states.
— By Sylvie Corbet in Paris.
The British prime minister's office says Theresa May and German Chancellor Angela Merkel have agreed on "the importance of ensuring Britain's orderly withdrawal from the European Union."
The two leaders held talks in Berlin as May tries to win backing from EU leaders for a further delay to Brexit.
The prime minister wants the 27 other EU leaders to postpone Britain's departure until June 30, and for the U.K. to be able to leave sooner if Parliament manages to ratify an EU divorce deal.
Downing Street didn't indicate Merkel's view on the best length for any extension.
If EU leaders refuse to grant an extension when they meet in Brussels Wednesday, Britain faces a chaotic "no-deal" departure from the bloc on Friday.
May plans to meet French President Emmanuel Macron later in Paris.
British Prime Minister Theresa May has left the chancellery in Berlin after meeting for about an hour and a half with German Chancellor Angela Merkel as she seeks European leaders' approval for another delay to Brexit.
May and Merkel made no comment to reporters as they left together and embraced. Merkel waved to May as her car set off.
May was heading to Paris later Tuesday to meet French President Emmanuel Macron, who has appeared to take a tougher line on giving Britain more time.
The prime minister is meeting all 27 leaders of the other European Union countries in Brussels on Wednesday. She needs their approval for a second extension to Britain's membership of the EU; if they refuse, Britain faces a sudden and chaotic departure Friday.
Half a dozen of EU nations are seeking to meet ahead of Wednesday's summit to coordinate their approach to the request of Britain to further extend the Brexit deadline.
An official, who asked not to be identified because the informal meeting was not officially announced, said leaders of France, Netherlands, Ireland, Belgium, Sweden and Denmark would discuss options some hours ahead of Wednesday's dinner summit.
The nations involved all would be directly implicated by a cliff-edge no-deal Brexit.
"It should be seen as coordinating the viewpoints," the official said.
—By Raf Casert
British Prime Minister Theresa May has arrived at German Chancellor Angela Merkel's office in Berlin on a quest to secure the agreement of Britain's European Union partners to a further delay to Brexit.
May strode into the chancellery on a sunny Tuesday lunchtime for her meeting with Merkel, who came out to shake her hand for photographers. Merkel could be heard saying that "we ordered the best possible weather."
The two leaders were not scheduled to make any remarks to reporters. May will travel to Paris later Tuesday to meet French President Emmanuel Macron.
May will meet leaders of the EU's other 27 members in Brussels on Wednesday for a summit at which they will decide whether to allow Britain to delay its withdrawal beyond the current deadline, set for Friday. If they refuse, Britain faces a sudden and chaotic exit at the end of the week.
A senior member of Theresa May's government says cross-party talks aimed at breaking the impasse over Britain's divorce from the European Union are moving forward in a "genuine and sincere" way.
Justice Secretary David Gauke told the BBC that it's too early to say whether the talks between the government and opposition Labour Party will be successful but work is continuing to identify a compromise, two days before EU leaders decide whether to grant a further extension to the Brexit process.
If they refuse, Britain faces a sudden and chaotic departure on Friday, the current deadline set by the EU.
Gauke says people involved in the cross-party talks "are telling me that the process is being undertaken in a genuine and sincere way from both sides."
France is vowing that the 27 EU nations facing the United Kingdom in Brexit divorce proceedings will remain united at Wednesday's summit, where they need to agree whether to give Prime Minister Theresa May another deadline extension.
French European Affairs Minister Amélie de Montchalin said early Tuesday that the 27 will need commitments from May that the British government will continue to play a constructive role in EU decision-making if a long extension is to be granted.
"We have the question what role Britain wants to play" if a long extension of the deadline is granted, possibly to the end of the year. In Britain, some have threatened that the government should seek to undermine EU policymaking as a way to get more leverage for the U.K.
A senior German official is demanding "substantial steps" forward in Britain's Brexit standoff and insisting any delay must come with strict conditions, as Prime Minister Theresa May prepares to plead for more time in Berlin.
Michael Roth, Germany's deputy foreign minister, said as he arrived at a European Union meeting in Luxembourg Tuesday that "so far absolutely nothing has changed" and "we are in a very, very frustrating situation here."
May has asked for a new delay until June 30. The bloc's leaders are due to meet Wednesday to consider the request. May is visiting Berlin and Paris later Tuesday.
Roth said that "within the European Union, there isn't an endless readiness to keep talking about delays so long as there is no substantial progress on the British side."