Islamabad: Pakistan on late Thursday shut down the Torkham border crossing with Afghanistan for an indefinite period of time after a suicide bomber attacked a crowded Sufi shrine in the southern part of the country, killing at least 70 people and wounding dozens more.
It is the busiest port of entry between the two countries, serving as a major transporting, shipping, and receiving site.
In past attacks, Islamabad has accused Kabul of harbouring Pakistani militants. Kabul also regularly points the finger at Pakistan for sending militants to carry out bombings in the war-torn country.
The Islamic State group (IS) claimed the attack, the deadliest to hit Pakistan so far in 2017, in the town of Sehwan in Sindh province, some 200 kilometres (124 miles) northeast of the provincial capital Karachi.
A police source said a suicide bomber entered the shrine of Lal Shahbaz Qalandar, a 13th-century Muslim saint, and blew himself up among hundreds of devotees.
The centuries-old shrine, one of the most revered in Pakistan, had been crowded on a Thursday, considered a sacred day for prayers.
Provincial health minister Sikandar Ali Mandhro said at least 70 people had died while 250 were wounded, 40 of them critically.
Images of the shrine showed blood smeared on the white floor around the grave, with debris and shoes scattered around.
Survivors and local residents, many in tears, were helping the blood-soaked wounded onto stretchers, while at Sehwan`s overcrowded medical facility the injured were being treated on floors and in corridors.
Emergency services are basic in Sehwan, with the nearest main hospital some 130 kilometres away.
"Many wounded people are in critical condition and they will be shifted to Karachi as soon as Navy helicopters and C-130 plane reach the nearest airport," Inspector General of Police for Sindh province AD Khawaja told AFP.
Prime Minister Nawaz Sharif said an attack on Sufis was considered a "direct threat", while military chief General Qamar Javed Bajwa warned: "Each drop of (the) nation`s blood shall be revenged, and revenged immediately. No more restraint for anyone."
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 in a bomb blast at the Shah Noorani shrine in Balochistan province in November last year.
Analysts have said IS is still scrabbling for purchase in Pakistan despite several high-profile attacks, and officials claim it is on the retreat in Afghanistan."To attack peaceful worshippers in one of their sacred spaces is shameful and cowardly," US ambassador David Hale said in a statement, while the European Union expressed its condolences to the victims.
Pakistanis vented their anger and grief on social media, with users calling the shrine a "capital of spirituality" and a "seat of interfaith harmony".
Pakistan has seen a dramatic improvement in security in the past two years, but a series of attacks this week -- most claimed by the Pakistani Taliban -- has undermined the growing sense of optimism.
Jamaat-ul-Ahrar, a faction of the Pakistani Taliban, said it had carried out a suicide bombing in Lahore which killed 13 people and wounded dozens more Monday, days after the group had vowed to launch a fresh offensive. Police and troops were also hit in attacks Thursday before and after the shrine bombing. An IED struck a military convoy in Balochistan, killing three soldiers, while gunmen on motorcycles killed four policemen and a civilian in the northwestern town of Dera Ismail Khan.
Four suicide bombers had struck northwest Pakistan on Wednesday, killing six people and unnerving civilians further.
"The past few days have been hard, and my heart is with the victims. But we can`t let these events divide us, or scare us," Sharif said in his statement.
"We have faced tougher circumstances, and still persevered."
The attacks underscore Pakistan`s struggle to stamp out extremism, which was stepped up after the country`s deadliest ever attack, a Pakistani Taliban assault on a school in Peshawar in 2014 which left more than 150 people dead -- mostly children.
(With Agency inputs)