In this Sunday, Feb. 22, 2015, file photo, Syrian Kurdish militia members of YPG make a V-sign next to poster of Abdullah Ocalan.

A Kurdish militia that has been backed by U.S.-led air strikes in Syria has joined a new military alliance that includes Arab groups, a statement released overnight said.

The alliance calling itself the Democratic Forces of Syria includes the Syrian Kurdish YPG militia and Syrian Arab groups that have already fought alongside it against ISIS in northern Syria.

It comes soon after the U.S. announced a shake-up of its support to Syrian rebels fighting ISIS, effectively ending its programme to train fighters outside Syria and focus instead on providing weapons to groups whose commanders have been U.S.-vetted.

The YPG has to date proved the most effective partner on the ground for U.S.-led air strikes against ISIS, taking large amounts of territory from the militants in northeast Syria this year.

“The sensitive stage our country Syria is going through and rapid developments on the military and political front … require that there be a united national military force for all Syrians, joining Kurds, Arabs, Syriacs and others groups,” said the statement, which was sent to Reuters by a YPG spokesman.

The Democratic Forces of Syria includes the YPG, various Arab groups including Jaysh al-Thuwwar (Army of Rebels), and an Assyrian Christian group.