Kalla Moutari says the attack occurred Wednesday at the Foraco water well site in Toumour, a village some 30 kilometers (18 miles) from the border in the Diffa region. He says the seven killed were Nigerien workers with the Foraco group.
Moutari says the attackers arrived on horses and seized two pickup trucks before heading toward Nigeria. The Nigeria-based Boko Haram has killed thousands of people over the years in the region that includes Chad and Cameroon.
Those countries, including Niger, contribute to a multinational force set up to fight Boko Haram.