At least 20 children among the victims of 'well-planned' bombing in Sehwan

Pakistan launched a nationwide security crackdown on Friday after a bomb ripped through a crowded Sufi shrine, killing 88 people and leaving hundreds wounded.

Police cordoned off the shrine of Lal Shahbaz Qalandar, a 13th century Muslim saint, as forensic investigators reached the town of Sehwan in Sindh province, some 200 kilometers northeast of financial hub Karachi.

Prime Minister Nawaz Sharif and army chief Qamar Javed Bajwa visited hospitalized victims and wished them a speedy recovery.

Sharif also directed hospital authorities to provide the best possible treatment to the injured.

The shrine's centuries-old white floor was still smeared with blood, along with scattered debris including shoes, shawls, and baby bottles.

At least 20 children are believed to be among the dead, said Moeen Uddin Siddiqui, head of local medical facility.

At 3:30 am, the shrine's caretaker stood among the carnage and defiantly rang its bell, a daily ritual that he vowed to continue, saying he "will not bow down to terrorists".

The Islamic State group has claimed responsibility for the attack, which came after a series of bloody extremist assaults this week, including a powerful Taliban suicide bomb in the eastern city of Lahore that killed 13 people.

The attacks have dented growing optimism in security after Pakistan's decade-long war on militancy.

Military spokesman Asif Ghafoor said the "well-planned attacks" were carried out from sanctuaries in Afghanistan, and Kabul has been asked to take action.

He also said the military had closed the border between the two countries, where Kabul and Islamabad have long accused each other of harboring extremists.

"Scores of suspects have been arrested in different cities in a pre-dawn crackdown," a government official said.

Security officials said at least 37 terrorists had been killed in the country's northwest in recent days.

Three days of mourning

The Sindh provincial government announced three days of mourning as Pakistanis vented their grief and fury on social media.

"Sunnis, Shias, Hindus, ppl from all faiths visit Sehwan often to pay homage to the great saint. This is an attack on our identity & culture," said Twitter user Zahraa Saifullah.

Sufism, a mystic Islamic order that believes in living saints, worships through music and is viewed as heretical by some hardline groups.

The Sunni jihadist IS group has targeted Sufi shrines in Pakistan previously, killing more than 50 at a shrine in Balochistan province last year.

Critics have long argued the military and government crackdown does not address the root causes of extremism, and groups such as the Taliban and the Islamic State group can still carry out spectacular attacks.

Chinese leaders express condolences

Chinese leaders on Friday strongly condemned the terrorist attack in Pakistan and offered support to the country in its fight against terrorism.

President Xi Jinping said in a message to his Pakistani counterpart Mamnoon Hussain that he has great sympathy for the massive casualties caused by the blast. "I condemn this terrorist attack, express my condolences to the victims and sincere sympathies to the injured and bereaved," Xi said.

China opposes terrorism in all forms, said the president, adding that Beijing will continue to support Pakistan's efforts to fight terrorism.

Premier Li Keqiang, on behalf of the Chinese government, also condemned the attack. "We unequivocally condemn terrorism in all forms and manifestations," Li said in a message to Pakistani Prime Minister Nawaz Sharif.

Mourners gather outside the closed gate of a shrine in Sehwan, Pakistan, after a terrorist bombing left 88 dead and hundreds wounded. Sif Hassan / Agence Francepresse