WRAPUP 22-Dozens of civilians, at least 13 U.S. troops killed in Kabul airport attack

(Adds U.S. toll increases to 13, comments from head of U.S. Central Command)

* Blasts leave dozens of bodies, wounded victims

* Western nations had warned of Islamic State threat

* Pentagon spokesman calls it a 'complex attack'

* U.S. to shift focus to getting last troops out

Aug 26 (Reuters) - Islamic State struck the crowded gates of Kabul airport in a suicide bomb attack on Thursday, killing scores of civilians and at least 13 U.S. troops, disrupting the airlift of tens of thousands of Afghans desperate to flee.

Kabul health officials were quoted as saying 60 civilians were killed. Video shot by Afghan journalists showed dozens of bodies strewn around a canal on the edge of the airport. At least two blasts rocked the area, witnesses said.

Islamic State said one of its suicide bombers targeted "translators and collaborators with the American army". U.S. officials also blamed the group.

The American casualties, which increased to 13 from 12 later on Thursday according to U.S. officials, were believed to be the most U.S. troops killed in Afghanistan in a single incident since 30 personnel died when a helicopter was shot down in August 2011.

The attack was carried out as U.S. forces raced to complete their withdrawal from Afghanistan, after President Joe Biden said the United States had long ago achieved its original rationale for invading the country in 2001: to root out al Qaeda militants and prevent a repeat of the Sept. 11 attacks on the United States.

Biden vowed to go after the perpetrators of Thursday's bombing and said he had ordered the Pentagon to plan how to strike ISIS-K, the Islamic State affiliate that claimed responsibility.

"We will not forgive. We will not forget. We will hunt you down and make you pay," Biden said during televised comments from the White House.

Corpses were in the canal by the airport fence, video from the scene showed, some being fished out and laid in heaps while wailing civilians searched for loved ones.

"For a moment I thought my eardrums were blasted and I lost my sense of hearing. I saw bodies and body parts flying in the air like a tornado blowing plastic bags. I saw bodies, body parts, elders and injured men, women and children scattered," said one Afghan who had been trying to reach the airport. "That little water flowing in the sewage canal had turned into blood."

The U.S. deaths were the first in action in Afghanistan in 18 months, a fact likely to be cited by critics who accuse Biden of recklessly abandoning a stable and hard-won status quo by ordering an abrupt pullout.