An Afghan Taliban delegation based in Qatar is in Karachi for direct talks with the Afghan government, BBC Urdu reported, citing diplomatic sources in Islamabad.

The Foreign Office has denied knowledge of the delegation's visit.

Following a deadly insurgent attack targeting a security services office in the heart of Kabul ─ one of the deadliest attacks in the Afghan capital since the Taliban were ousted from power in 2001 ─ observers have said Pakistan is pressuring the Taliban to join peace talks, BBC Urdu reported.

Taliban representatives in Pakistan will join the Afghan government at the table during the negotiating process.

The development comes as Afghan President Ashraf Ghani threatened diplomatic reprisals against Pakistan if it refuses to take action against the Taliban, in a new hard-line stance after the Kabul attack left 64 people dead.

The attack cast a pall over international efforts in recent months to jumpstart Pakistan-brokered peace talks, which stalled last summer after the Taliban belatedly confirmed the death of their leader Mullah Omar.

"I want to make it clear that we no longer expect Pakistan to bring the Taliban to the negotiating table," Mr Ghani said in a sombre address to both houses of the Afghan parliament.

"But we want Pakistan to fulfil its promises ... and take military action against their sanctuaries and leadership based on its soil. If they can’t target them, they should hand them over to our judiciary. If we do not see a change, despite our sincere efforts for regional cooperation, we will be forced to turn to the UN Security Council and start serious diplomatic effort," Ghani said.

Ghani’s remarks reflect his frustration after he expended substantial political capital since coming to power in 2014 in courting Pakistan in the hope of pressuring the militants to the negotiating table.

The Pakistani government recently admitted, after years of official denial, that the Afghan Taliban leadership enjoys safe haven inside the country.

He said Taliban leaders sheltering in Peshawar and Quetta were "slaves and enemies of Afghanistan who shed the blood of their countrymen".

He did not say whose slaves he thought the Taliban were. "There are no good or bad terrorists ... Pakistan should act on them as a responsible government," Ghani said.

The Afghan president vowed a tough military response against the insurgents and pledged to enforce legal punishments, including executions of convicted militants.

"The time for amnesty is over," he said. "For the Taliban who are ready to end bloodshed, we have left the door open for talks. But the door will not be open forever."