The joint statement Thursday from the U.S., France, Italy, the United Arab Emirates and the United Kingdom comes after Libyan army commander Khalifa Hifter ordered his forces to march on Tripoli, the capital of the U.N.-backed government.
The five nations say that "at this sensitive moment in Libya's transition, military posturing and threats of unilateral action only risk propelling Libya back toward chaos." They say military action is "hindering prospects for UN political mediation." Upcoming peace talks brokered by the United Nations are aimed at drawing a roadmap for new elections.
Libya split between rival governments in the east and west after descending into chaos following the 2011 NATO-supported uprising that toppled Moammar Gadhafi.
A Libyan army spokesman says forces marching on Tripoli are giving militiamen in control of the capital the option of surrendering or staying home.
Spreading out a map during a news conference on Thursday, Ahmed al-Mesmari showed positions from which the so-called Libya National Army were deployed and marching toward Tripoli.
The towns are mostly in the south and west of Tripoli, which is under control of a U.N.- backed government and aligned militias.
"You choose between staying home, handing over your weapons, or raising the white banner," he said, addressing the militias in control of Tripoli.
U.N. Secretary-General Antonio Guterres has urged Libya's warring factions to de-escalate during his visit to the country, shortly after a top commander ordered his forces to march on to Tripoli.
Guterres tells reporters in Tripoli on Thursday that there is no military solution to Libya's war and that for the sake of the upcoming peace conference this month among Libyan factions, de-escalation is needed.
He says: "There can't be national conference in these circumstances."
Libyan army commander Khalifa Hifter in an audio recording posted online has ordered his forces to march to Tripoli, the capital of the U.N.-backed government.
Hifter, who commands the so-called Libya National Army based in the east, described his forces' move as a "victorious march" to "shake the lands under the feet of the unjust bunch."
He ordered forces not to open fire on any civilians saying, "whoever raises the white banner is safe."
His forces have taken over the town of Gharyan, 50 kilometers (31 miles) from Tripoli.
The U.N. chief says he's worried about a major armed showdown in Libya and is urging warring factions to instead turn to dialogue.
Antonio Guterres' remarks came as Libyan forces loyal to strongman Khalifa Hifter entered the town of Gharyan, about 50 kilometers, or 31 miles, south of the capital. It's the closest to Tripoli that Hifter's fighters reached in their campaign westwards from the country's east.
Guterres posted on Twitter on Thursday that he's "deeply concerned by the military movement taking place in Libya and the risk of confrontation."
He added: "There is no military solution. Only intra-Libyan dialogue can solve Libyan problems."
Guterres arrived in Libya on Wednesday — the first U.N. chief to visit since the 2011 uprising that toppled and later killed long-time ruler Moammar Gadhafi.