Pakistan has told Britain to pull out some of its military trainers, in what appears to be the latest sign of strained relations with the West after last month's killing of Osama bin Laden by US troops.

Pakistan's military faces its most severe crisis in decades following the May 2 raid in which the al-Qaida leader was killed on Pakistani soil by foreign soldiers.

"The UK has been asked to withdraw some of its training support teams on a temporary basis by the Pakistani government in response to security concerns," British High Commission spokesman in Islamabad, George Sheriff, told Reuters on Monday.

He said the Pakistan authorities had warned about "security concerns" but he did not elaborate.

The Guardian daily quoted the British Defence Ministry as confirming the withdrawal of at least 18 military advisers who were helping train a poorly equipped paramilitary force, the Frontier Corps, in counter-terrorism.

Since the May 2 raid, Pakistan has been keen to demonstrate its independence from its Western sponsors and has also drastically scaled back the number of military trainers from its main backer, the United States.

The number of US trainers has been reduced to less than 50 from about 120, Pakistani and American officials have said.

The reductions are a signs of a strained alliance that Washington still sees as critical to its success in the war in neighbouring Afghanistan as well as the fight against al-Qaida and its affiliates.

The raid on bin Laden's compound in Abbottabad, 30 miles (50 km) northwest of Islamabad, intensified US questions about Pakistan's possible role in sheltering militants.

The army still enjoys high approval ratings in Pakistan, but its critics blame it for cultivating Islamist militants in the past for use against arch-rival India, who are now increasingly slipping out of its control and turning on Pakistani authorities.

The Frontier Corps has also come in for criticism. The Guardian reported that it has been accused of human rights violations in Baluchistan province, where a decades-long separatist insurgency is simmering.

Pakistani newspapers have reported at least 170 Baluch nationalists have disappeared and five unarmed Chechens were shot to death in May at a checkpost in the provincial capital, Quetta. The government says it is investigating.

The Guardian reported that the British trainers had been based near Quetta in Baluchistan at a British-funded base, working alongside six American advisers training batches of 360 recruits in 12-week courses.