By Mirwais Harooni and Kay Johnson

KABUL (Reuters) - A suicide car bomber killed two U.S. troops and a Polish soldier in an attack on a convoy near the U.S. embassy in Kabul on Tuesday, the NATO-led coalition said, one of the worst attacks on international forces in the Afghan capital in months.

The attack near the heavily fortified embassy wounded 13 Afghan civilians nearby. It came amid a months-long political stalemate and an emboldened insurgency, with a presidential election still unresolved as most foreign combat troops prepare to leave by the end of the year.

The Taliban claimed responsibility for the bombing on the main road leading to Kabul's international airport, not far from the sprawling U.S. embassy compound that is also home to other members of the NATO-led International Security Assistance Force (ISAF) coalition.

In a text message to journalists, a Taliban spokesman said the suicide bomber, identified only as Bilal, had been lying in wait for foreign troops in a car packed with explosives.

Two of the three killed were American military personnel, a U.S. Defence Dept. official confirmed on Tuesday in Washington.

Poland's military identified the third victim as Rafal Celebudzki, a platoon commander who had also served in Iraq. Two other Polish soldiers were wounded.

Afghan Deputy Interior Minister Mohammad Ayub Salangi said on Twitter a suicide car bomber had targeted a convoy of vehicles carrying foreign troops.

The blast tore through cars and shattered shop windows on the road a few hundred metres from the main embassy gate.

Kabul police spokesman Hashmat Stanekzai said 13 Afghan civilians were wounded and 17 nearby cars damaged.

"HUGE BLAST"

Ambulances arrived within minutes of the blast during the morning rush hour at about 8 a.m. (0330 GMT).

"It was a huge blast," said wounded bystander Haji Awal Gul, his shirt splattered with blood as he stood on the roadside.

Tensions have been building in Afghanistan since the disputed run-off vote in a presidential election in June, with rival candidates still arguing over the outcome despite U.S. efforts to broker a compromise deal.

Story continues

Taliban insurgents have been exploiting the uncertainty, launching bombings and attacks on government security forces and officials across Afghanistan.

In western Herat province, one U.S. soldier was killed when an unidentified member of the Afghan security forces turned on his trainers late on Monday, the latest incident in a string of "green-on-blue" attacks.

A Western official, who asked not to be identified, said the U.S. soldier was killed when the Afghan threw a hand grenade at his trainers.

ISAF did not confirm the exact details of the attack. An ISAF statement on Tuesday said the U.S. service member was killed when an individual wearing an Afghan army uniform "turned his weapon against ISAF members".

Also overnight, two suicide bombers set ablaze 26 fuel tankers in an attack on a customs post in eastern Afghanistan near a border crossing into Pakistan, Afghanistan's TOLO media reported on Tuesday.

One of the attackers detonated explosives he was carrying while the other was killed in an ensuing gunbattle, the report on TOLOnews.com quoted Afghan officials as saying.

(Additional reporting by Missy Ryan in Washington and Jessica Donati in Kabul; Editing by Paul Tait and Clarence Fernandez)