WASHINGTON - US forces in Somalia said Friday that four Al-Shabaab militants were killed in an airstrike as part of the ongoing offensive against the jihadist rebels. The US Africa Command said the strike took place on Thursday in southern Somalia, around 50 kilometers (30 miles) northwest of the port city of Kismayo. Africa Command did not provide details on the attack, which it said was undertaken "in coordination with the Federal Government of Somalia." But it said no civilians were killed. "US forces will continue to use all authorized and appropriate measures to protect US citizens and to disable terrorist threats," US Africa Command said in a statement.