KABUL (Reuters) - The Islamic State militant group claimed responsibility on Sunday for a suicide blast at a wedding reception in Afghanistan that killed 63 people, underlining the dangers the country faces even if the Taliban agrees to a pact with the United States.

The Saturday night attack came as the Taliban and the United States try to negotiate an agreement on the withdrawal of U.S. forces in exchange for a Taliban commitment on security and peace talks with Afghanistan’s U.S.-backed government.

Islamic State fighters, who first appeared in Afghanistan in 2014 and have since made inroads in the east and north, are not involved in the talks. They are battling government and U.S.-led international forces and the Taliban.

The U.S. special envoy for reconciliation in Afghanistan, Zalmay Khalilzad, said the attack showed the need to accelerate efforts to reach a deal with the Taliban, to help defeat Islamic State.

U.S. President Donald Trump on Sunday called the attack “horrible” and expressed optimism at the state of talks. He said the United States would seek to get troop levels below 13,000 but leave “very significant” intelligence capabilities behind.

“We’re there for one reason, we don’t want that to be a laboratory, it can’t be a laboratory for terror,” Trump said, speaking before boarding Air Force One in New Jersey.

About 14,000 U.S. troops remain in Afghanistan, training and advising Afghan security forces and conducting counterinsurgency operations.

Islamic State has claimed some of the bloodiest attacks in Afghan cities over the past couple of years, with some aimed at the Shi’ite minority.

The Sunni Muslim group, in a statement on the messaging website Telegram, claimed responsibility for the attack at a west Kabul wedding hall in a minority Shi’ite neighborhood, saying its bomber had been able to infiltrate the reception and detonate his explosives in the crowd of “infidels”.

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The Taliban earlier denied responsibility for the blast and condemned it.

More than 180 people were wounded, with many women and children among the casualties, interior ministry spokesman Nasrat Rahimi said on Sunday as grieving families thronged to Kabul’s crowded cemeteries.

“We want peace, not such brutal suicide attacks,” said Ahmad Khan, who was burying a relative.

Pictures on social media from the scene of the blast showed bodies strewn amid overturned tables and chairs, with dark blood stains on the wedding hall carpet.

Both the bride and groom survived.

“I won’t ever be able to forget this, however much I try,” the groom, Mirwais Elmi, told the TOLOnews channel.

He said his cousin and some friends had been killed.

The bride’s father told TOLOnews that 14 members of his family were killed.

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BLOODSHED AND TALKS

Brightly lit wedding halls that line some suburban streets of the city had been targeted previously by bombers. At least 40 people were killed in a blast in November.

There has been no let-up in fighting and bomb attacks in Afghanistan over recent months despite talks between the United States and the Taliban since late last year.

President Ashraf Ghani, in comments on the Kabul blast before the Islamic State claim, said the Taliban could not “absolve themselves of blame for they provide a platform for terrorists”.

Celebrations for Monday’s 100th anniversary of Afghanistan’s independence from Britain were curtailed out of respect for the blast victims, the president’s office said.

The Taliban has been fighting to expel foreign forces and re-establish a theocratic Islamic state since its ousting in October 2001, weeks after the Sept. 11 attacks on the United States.

Both U.S. negotiators and the Taliban have reported progress after eight rounds of talks since late last year.

Trump has made no secret of his desire for a U.S. pullout from Afghanistan and an end to America’s longest war.

But there are concerns among Afghan officials and U.S. national security aides that Afghanistan could be plunged into a new civil war that could herald a return of Taliban rule and international militants, including Islamic State, finding a refuge.

Afghan government officials also fear that a Taliban pact could drive some die-hard Taliban fighters into the arms of Islamic State.

Under the expected deal, the Taliban, in exchange for a U.S. commitment to withdraw, would guarantee that Afghanistan would not be a sanctuary for militants to expand and plot new attacks.

The United States also wants a Taliban commitment to hold power-sharing talks with the government and announce a ceasefire. The Taliban has refused to talk to the government.

Khalilzad said the peace process had to be accelerated, in particular the intra-Afghan talks.

“Success here will put Afghans in a much stronger position to defeat ISIS,” he tweeted, referring to Islamic State.