The United Nations and Britain said on Thursday that they will withdraw the children of international staff from Pakistan in the wake of the deadly bombing of the Marriott Hotel in Islamabad.

The move comes despite increased security measures by Pakistani authorities after last month's attack, in which 60 people were killed, and reinforces fears that Taliban and al-Qaeda militants are destabilising the country.

Nuclear-armed Pakistan has faced a wave of suicide bombings by extremists based in the tribal areas bordering Afghanistan, while tensions are rising between Islamabad and Washington over US military incursions.

"The United Nations has raised the security level... which provides for the movement of dependent children," Fikret Akcura, the UN resident coordinator for Pakistan, told AFP.

"They can either go to a third country outside Pakistan or to their home country," Akcura said, adding that the UN would monitor the situation and would reduce the security level "when we find it is safe".

He did not say how many children would be affected. There was no immediate comment on the evacuation from the UN headquarters in New York or from the Pakistani government.

The British Foreign Office said separately overnight that more than 60 children of British diplomats will be withdrawn from Islamabad over the next few weeks, the Foreign Office said.

They are all aged under eight, as older children tend to attend boarding school in Britain.

"Following a review of security in the wake of the attack on the Marriott Hotel, the Foreign and Commonwealth Office has decided that the children of UK-based staff at the British High Commission in Islamabad should return to the UK," a spokesperson told AFP.

Any dependents, such as spouses, could return to Britain if they chose.

The spokesperson said the "core work of the High Commission will not be affected. The UK is committed to maintaining its strong relationship with Pakistan, especially at this difficult time."

"The attack on the Marriott Hotel reinforces our shared determination to tackle violent extremism," he added.

At present, Britain advises its citizens to avoid all non-essential travel to Islamabad, Rawalpindi, Karachi, Lahore and Peshawar, and cautions against using international hotels popular with Westerners.

Security has been tightened in Islamabad since the Marriott blast on 20 September, with concrete barriers and police roadblocks creating a so-called "red zone" around government buildings and the city's diplomatic area.

But the measures have not been enough to convince many diplomats, with further attacks feared. Other foreign embassies in the capital are considering whether to pull out children, diplomatic sources said.

Pakistani officials say they suspect al-Qaeda was behind the Marriott bomb and the extremist group's deputy leader Ayman al-Zawahiri in April described the UN as an "enemy of Islam and Muslims."

Pakistan is battling a wave of violence blamed on Taliban and al-Qaeda militants.

AFP