Rockets struck a coalition base in Basra, Iraq, on Thursday afternoon, killing two civilian contractors, the U.S. military said Friday. Eight other people — four coalition troops and four civilians — were wounded.

The nationalities of the dead and wounded were not given. British, U.S. and Iraqi forces all operate in Basra, the southern port city that saw large-scale violence beginning with a government crackdown on Shiite militias in late March.

After the rocket attack on Thursday, coalition troops fired counter-battery missions and an unmanned aerial vehicle identified rocket launcher rails and a suspicious vehicle. Helicopters destroyed the rails and vehicle with Hellfire missiles, officials said.

U.S. military officials said Friday the rocket attacks were the first indirect-fire attacks to cause casualties in Basra since March 27.

Late that month, Iraqi Prime Minister Nouri al-Maliki launched a sweeping offensive against Shiite militias in the city. Some 1,000 Iraqi security force members deserted or refused to fight, and U.S. commanders later criticized the attack plan.

U.S. and British officials claim that 70 percent of the city is now secured by Iraqi forces.