KABUL  - Three US-led coalition soldiers were killed in an explosion in southern Afghanistan on Thursday, the force said, taking to 17 the number of international troops to die in the country this month. The coalition did not give the nationalities of the soldiers or specify where they were killed in southern Afghanistan, which has seen some of the most violent attacks in a Taliban-led insurgency that has gained pace this year. "Three coalition service members were killed in an explosion while on a dismounted patrol in southern Afghanistan today," it said in a statement that gave no other details. Two rockets were fired at Afghanistan's main international airport in Kabul Thursday, injuring two civilians but causing little damage, the interior ministry said. The Interior Ministry said separately that two weeks of heavy fighting in the southern provinces of Kandahar and Helmand had left more than 20 policemen dead. Police on Thursday pulled back from two posts in Helmand's Nad Ali district under pressure from Taliban attacks launched two weeks ago, ministry spokesman Zemarai Bashary told AFP. "In the past two weeks we've lost 15 policemen in fighting with Taliban in Nad Ali. This morning we had to withdraw from two posts," he said. Six other policemen were killed and about 10 others were wounded in Ghorak district in neighbouring Kandahar province, also under attack by Taliban rebels, Bashary said. "The fighting in both places continues," Bashary said. Another police officer was meanwhile killed and three others were wounded when a roadside bomb - similar to those used by Taliban militants - struck the motorcade of a top police official in Logar province, just south of Kabul. Provincial police chief Ghulam Mustafa escaped unharmed from the attack, which came one day after Taliban militants killed three Western female aid workers in an ambush in Logar. The three employees of the International Rescue Committee were killed along with their driver when rebels opened fire on their vehicle on a road near the provincial capital Pul-i-Alam. The Taliban said its men had carried out the attack, but said those killed were female soldiers.