BEIRUT (AP) — Unidentified planes struck targets in Syria near the border with Iraq on Friday, reports said, triggering “a huge explosion” amid soaring tensions in the region between the U.S. and Iran.

The Syrian Observatory for Human Rights said the planes targeted positions belonging to pro-Iran militias in the Boukamal area, near the border with Iraq. The Britain-based organization which documents the war in Syria through a network of activists on the ground said the planes struck among other targets weapons depots and vehicles belonging to the militias.

It reported several explosions in the border area. Deir Ezzor 24, an activist collective that reports on news in the border area, said that the planes strikes struck trucks carrying weapons and depots for ballistic missiles in the area. Omar Abu Laila, a Europe-based activist from Deir el-Zour who runs the group, said the attack triggered “a huge explosion” heard in the Syrian-Iraqi border.

The Sound and picture, another activist collective in Syria's eastern Deir el-Zour area, said “unidentified planes" struck militia targets in Boukamal.

There was no immediate comment from Syria or Iraq, and the reports could not be independently confirmed.

The U.S. carried out military strikes in the area on Dec. 29, killing 25 members of an Iran-backed Iraqi militia in retaliation to a rocket attack on a military base in Iraq that killed a U.S. contractor. The U.S. blamed that attack on a Iranian-backed Iraqi militia.

Israel has also struck Iran-backed militias in the area in the past.

The reported airstrikes came days after a U.S. drone strike killed Iran’s most powerful general after he landed at Baghdad airport, drawing angry calls for revenge and escalating tensions to the brink of an all-out war between the two sides.

Iran responded by firing a barrage of missiles at military bases in Iraq that host U.S. troops. Since then, both sides have signaled they were stepping back from further escalation but tensions remain high and the region on edge.

Amid the soaring tensions, Russian President Vladimir Putin made a rare visit to Syria this week for talks with President Bashar Assad in Damascus. Russia has been a key ally for Assad, offering crucial military and political backing throughout the country’s civil war.

The area struck Friday is key to a land corridor for Tehran that links Iran across Iraq and Syria through Lebanon. The Observatory report on Friday claimed that Putin had informed Assad during the visit of a U.S. intention to “close” the land corridor for good.