A Pakistani doctor who helped the US track down Osama bin Laden has been convicted of high treason and sentenced to 33 years in prison, according to a government official.

Shakil Afridi was also ordered to pay a fine of about 3,500 US dollars (£2,200), said Nasir Khan. If Afridi doesn't pay, he will spend another three and half years in prison.

Mr Khan is a government official in Pakistan's Khyber tribal area, where Afridi was tried.

Afridi ran a vaccination programme for the CIA to collect DNA and verify bin Laden's presence at the compound in the town of Abbottabad, where he was killed last May by US commandos.

US secretary of state Hillary Clinton has called for Afridi to be released, saying his work served Pakistani and American interests.

Afridi's conviction comes at a sensitive time because the US is already frustrated by Pakistan's refusal to reopen Nato supply routes to Afghanistan.

The supply routes were closed six months ago in retaliation for American air strikes that killed 24 Pakistani soldiers.

Afridi was tried under the Frontier Crimes Regulations, the set of laws that govern Pakistan's semi-autonomous tribal region.

Human rights organisations have criticised the regulations for not providing suspects due process of law. There is no right to legal representation, to present material evidence or cross-examine witnesses. Verdicts are normally handed down by a Khyber government official in consultation with a council of government elders.

Afridi has the right to appeal against the verdict, said Iqbal Khan, another Khyber government official.

Afridi was detained some time after the raid on May 2 last year, but the start of his trial was never publicised.

"He was working for a foreign spy agency. We are looking after our national interests," said a Pakistani intelligence official.

The US operation that killed bin Laden severely strained ties with Pakistan. The Pakistani government kicked out US military trainers and limited counter-terrorism co-operation with the CIA.

The relationship got worse in November when the US killed 24 Pakistani soldiers at two posts along the Afghan border, an attack that Washington said was an accident but the Pakistani army insisted was deliberate.

Pakistan retaliated by closing the Nato supply routes and kicking the US out of a base used by American drones. Before the attack, the US and other Nato countries fighting in Afghanistan shipped about 30% of their non-lethal supplies through Pakistan. Since then, the coalition has used more expensive routes through Russia and Central Asia.

The US has pressed Pakistan to reopen the supply line, but negotiations have been hampered by Washington's refusal to apologise for the attack and stop drone strikes in the country as demanded by Pakistan's parliament. Many observers view the latter demand with scepticism because elements within Pakistan's government and military have supported the attacks in the past.