The United States conducted an airstrike on Wednesday against Taliban fighters in Afghanistan's southern Helmand province, a US forces spokesman said, the first such attack since a troop withdrawal agreement was signed between the two sides on Saturday.The Taliban fighters were "were actively attacking an (Afghan National Security Forces) checkpoint. This was a defensive strike to disrupt the attack," said Colonel Sonny Leggett, a spokesman for the US Forces in Afghanistan in a tweet.He said Washington was committed to peace but would defend against Afghan forces if needed."Taliban leadership promised the (international) community they would reduce violence and not increase attacks. We call on the Taliban to stop needless attacks and uphold their commitments," he said.The airstrike was the first by the United States against the Taliban in 11 days, when a reduction in violence agreement had begun between the sides in the lead up to Saturday's pact.Since the signing, the Taliban had decided on Monday to resume normal operations against Afghan forces, though sources have said they would continue to hold back on attacks on foreign forces.The Taliban has so far declined to confirm or deny responsibility for any of the attacks and did not immediately respond to request for comment on the airstrike.On Tuesday, there were several attacks against Afghan officials blamed on the Taliban, including one at a security checkpoint near a copper mine that killed five Afghan policemen.A Ministry of Defence spokesman said on Wednesday that in the past 24 hours there had been clashes between the Taliban and Afghan security forces in nine provinces, including Helmand.A spokesman for Helmand's provincial governor said that the Taliban had attacked a security checkpoint in Washer district - a different district to the one in which the US carried out its airstike - on Tuesday evening, killing two police officers.A defense ministry spokesman also confirmed an attack against an Afghan army base in the city of Kunduz and said there were seven casualties.The weekend agreement envisages a full withdrawal of all US and coalition forces within 14 months, dependent on security guarantees by the Taliban, but faces a number of hurdles as the United States tries to shepherd the Taliban and Afghan government towards talks.