A suicide bomb attack killed two American troops in Afghanistan on Wednesday as they were travelling in a convoy near the airport in the southern city of Kandahar, the U.S. military said, in a strike claimed by the Taliban insurgency.

The attack was a reminder of the dangers posed to the 8,400 U.S. forces in Afghanistan as President Donald Trump weighs sending thousands more troops to America's longest war.

The goal would be to better assist Afghan forces, who are locked in a stalemate with a resurgent Taliban after nearly 16 years of conflict. A mid-July deadline set by the Pentagon to complete its war strategy has come and gone and Trump's own views on the Afghan war remain unclear.

Pentagon spokesman Navy Captain Jeff Davis announced the deaths from Washington. He gave no further details and the Pentagon declined comment on any wounded.

One U.S. official, speaking on condition of anonymity, said there could also be several NATO-led coalition wounded in the attack but did not provide a number.

A local security official said the attacker drove an explosives-laden vehicle into the convoy. Photos of the site showed one partially destroyed armoured vehicle, with the rear of the truck particularly badly damaged.

The Taliban claimed responsibility for the attack in an online post by spokesman Zabihullah Mujahid. He said the explosion destroyed two vehicles and killed 15 foreign soldiers, including two "high-ranking officers".

A Reuters witness said military helicopters landed at the site at least four times as responding troops secured the area and removed the damaged vehicle.

The airport in Kandahar is home to a major military base for international troops helping Afghan security forces in their struggle to contain the Islamist Taliban insurgency.

The coalition maintains nearly 13,000 troops from 39 countries as part of a mission to train, advise and assist Afghan troops.

U.S. military commanders in Afghanistan have asked for several thousand additional troops but the request is stalled in Washington, where Trump has expressed scepticism over extending the U.S. commitment.