The United Nations and the US have condemned the suicide attack in Pakistan that killed 54 people and said terrorism in all its forms and manifestations is unjustifiable and an affront to peaceful and democratic societies.

At least 54 people were killed and over 100 injured in the attack on Sunday when more than 400 members of the conservative Jamiat Ulema Islam-Fazl (JUI-F) party, known for its links to hardline political Islam, had gathered for a meeting under a large tent in Khyber Pakhtunkhwa's Khar town, which borders Afghanistan.

The banned terrorist group Islamic State (ISIS) has claimed responsibility for the suicide attack.

UN General Assembly President Csaba Korosi said strongly condemns the suicide attack in Khyber Pakhtunkhwa Pakistan, his spokesperson told reporters at the UN headquarters in New York.

“The President conveys his deepest sympathy and condolences to the families of the victims, the Government and the people of Pakistan. Terrorism in all its forms and manifestations is criminal and unjustifiable, regardless of its motivation, wherever, whenever and by whomsoever commits it,” he said.

Korosi urges the international community to strengthen its efforts to combat the scourge of terrorism, and to bring the perpetrators to justice, the spokesperson said.

UN Secretary-General Guterres has also extended his heartfelt condolences to the families of the victims and wished a prompt recovery to the wounded.

"The UN chief also called on the Pakistani authorities to bring those responsible to justice," UN Deputy Spokesperson Farhan Haq told reporters in New York on Monday.

“The Secretary-General denounces all instances of terrorism and deliberate targeted attacks against civilians and stands in solidarity with the government and the people of Pakistan in combating this scourge,” he said.

US State Department Spokesperson Matthew Miller, at a separate briefing here, condemned the attack in northwestern Pakistan.

“We are deeply saddened by the loss of life and injuries sustained from the explosion and share our heartfelt condolences with those affected by the attack,” he told reporters in Washington on Tuesday.

“The Pakistani people have suffered greatly at the hands of terrorists. We believe in the resilience of Pakistan’s people and their capacity to recover from this devastating attack. No country should have to suffer such acts of terror, which are an affront to all peaceful and democratic societies,” he said.

The United States remains committed to working with Pakistan to address the shared threat posed by terrorist groups throughout the region and support Pakistani efforts to combat terrorism in a manner that promotes the rule of law and the protection of human rights, he said.

The suicide bombing on Sunday came hours before Chinese Vice Premier He Lifeng arrived in Islamabad, where he signed six new agreements to boost trade and economic ties to mark a decade of the USD 60 billion China-Pakistan Economic Corridor on Monday.

The attack in Bajaur district on Sunday was one of the worst in northwestern Pakistan in the last decade.

In 2014, nearly 150 people, mostly schoolchildren, were killed in a Taliban attack on an army-run school in Peshawar.

On January 30 this year, a Pakistan Taliban suicide bomber blew himself up during the afternoon prayers in a mosque in Peshawar, killing 101 people and injuring more than 200.

Responding to a question, Miller said the US has made it clear to the Taliban that it is important they do not allow Afghanistan to be used as a base for terrorist attacks in the region or anywhere else.

The US funds several counterterrorism capacity-building programmes in Pakistan focused on law enforcement and the justice sector and will continue to do so, he said.

“Our support for Pakistan’s economic success is unwavering. We’ll continue to engage with Pakistan about strengthening our trade and investment ties, all of which are priorities for our bilateral relationship,” Miller said.

On China-Pakistan Economic Corridor (CPEC), Miller said with respect to investments by any country, the US believes good governance, long-term capacity building, and sustainable market-based approaches that allow the private sector to flourish are the best paths to sustained growth and development.

“We welcome trade and investment that promotes such development and growth. But we will continue, in all cases, to emphasise the need for transparency, sustainable financing practices, and preservation of national and data security to ensure mutual benefit for both Pakistan and its partners.

"We have not always seen that with respect to investments by the PRC (People’s Republic of China) in countries around the world. But if investments that promote transparency and responsible debt management, we believe are appropriate,” Miller said.

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