By Steve Holland and Trevor Hunnicutt
WASHINGTON (Reuters) -President Joe Biden, anxiously seeking to complete the U.S. evacuation from Afghanistan, watched a nightmare scenario unfold on Thursday when suicide bomb explosions outside the Kabul airport killed at least 12 U.S. troops and wounded 15 others.
Biden had already gathered in the White House Situation Room with his top military and diplomatic advisers for a daily update on the chaotic evacuation effort early on Thursday when the blasts occurred outside the airport in the Afghan capital.
The team did not emerge from the Situation Room until more than two hours later, then Biden migrated to the Oval Office, as a steady stream of Pentagon personnel, some in uniform, filed in and out of the White House.
Some staff learned of the growing numbers of U.S. military dead from mounted television screens in the White House West Wing as the day progressed, and let out cries of despair as the numbers multiplied.
"We're outraged as well as heartbroken," Biden said of himself and his wife Jill in public remarks late on Thursday. The couple had "some sense what the families of these brave heroes are feeling today" after the death of his Army major son Beau from brain cancer, which Biden has previously linked to his son's military service.
He vowed to "hunt down" the attackers and called the dead troops "heroes."
"They were part of simply what I call the backbone of America, they are the spine of America. The best the country has to offer," Biden said.
Islamic State claimed responsibility for the attack which also killed scores of civilians.
Biden, facing criticism over the U.S. evacuation after the rapid Taliban takeover of Afghanistan as American forces were pulling out after two decades, has sought to hammer home a message in days before the attacks that the United States was leaving Afghanistan in order to save the lives of U.S. troops.
The U.S. military death toll in the Afghan war since 2001 is roughly 2,500.
Remaining any longer, the Democratic president told reporters on Aug. 20, could mean he would need to "send your sons, your daughters - like my son was sent to Iraq - to maybe die. And for what? For what?"
Thursday's U.S. military casualties were the first in Afghanistan since February 2020 and represented the deadliest day for American troops there in a decade.
'THE NIGHTMARE WE FEARED'
Some critics blamed the rushed evacuation, which threatens to leave some Americans behind in Afghanistan, for the deaths among the roughly 5,200 Americans providing security at Kabul's airport to close out U.S. involvement in Afghanistan after 20 years of conflict. U.S. officials said on Thursday about 1,000 Americans remained in Afghanistan.
"This is the nightmare we feared - and it's why for weeks, military, intelligence and congressional leaders from both parties have begged the president to stand up to the Taliban and push out the airport perimeter," Republican U.S. Senator Ben Sasse said.
"As we wait for more details to come in, one thing is clear: We can't trust the Taliban with Americans' security," added Democrat Bob Menendez, chairman of the Senate Foreign Relations Committee, in an implicit criticism of Biden's strategy.
Biden, who took office in January, pushed a May withdrawal target set by former President Donald Trump to Aug. 31. But, under pressure from Pentagon officials who warned that security risks from Islamist militants were rising at the airport, Biden refused to move it back further, despite pressure from allied nations.
A Biden adviser, speaking on condition of anonymity, said the deaths of American troops underscored both why Biden made the decision to withdraw in the first place and the risks of an extended engagement in the country.
There are further risks to the president, including worsening internal Democratic Party divisions that have been brewing, the adviser said.
Until now, the White House has tried to push back on hostile media coverage, the adviser said, by citing the lack of U.S. deaths in the evacuation effort.
A long-time skeptic of the 20-year military presence in Afghanistan, Biden has said the United States long ago achieved its original rationale for invading the country in 2001: to root out al Qaeda militants and prevent another attack on the United States like the one launched on Sept. 11, 2001.
The mastermind of that attack, al Qaeda leader Osama bin Laden, was killed by a U.S. military team in neighboring Pakistan in 2011. Afghanistan's Taliban rulers had harbored al Qaeda militants ahead of the 2001 attack before being toppled from power after the 2001 U.S.-led invasion.
After Trump orchestrated a peace deal with the Taliban before leaving office, Biden and his team stayed in constant contact with the group to try to ensure a smooth U.S. evacuation.
Due to the day's events, Biden was forced to postpone - at least until Friday - his first face-to-face meeting with Israeli Prime Minister Naftali Bennett and canceled a meeting with a bipartisan group of state governors about temporarily housing or helping resettle Afghan refugees.
(Reporting by Steve Holland, Trevor Hunnicutt, Nandita Bose and Idrees Ali; Editing by Heather Timmons, Will Dunham and Howard Goller)