WASHINGTON: The US State Department said that Pakistan had no basis to hold or charge a surgeon who was sentenced on Wednesday to 33 years in prison for helping in the hunt for Osama bin Laden.

A tribal court in Khyber, a lawless district and extremist hotbed, convicted surgeon Shakeel Afridi of treason after he agreed to collect DNA for US intelligence to verify the presence of the most-wanted al Qaeda leader.

State Department spokeswoman Victoria Nuland recalled that both US Secretary of State Hillary Clinton and US Defence Secretary Leon Panetta had earlier raised concerns with Pakistan about the doctor's case.

“Our views on it haven't changed. We continue to see no basis for Dr. Afridi to be held,” Nuland said. “We will continue to make those representations to the government of Pakistan.”

When asked why she only referred to Afridi's charges and did not acknowledge his actual conviction and sentencing, Nuland said: “It's not clear that the legal process is over, OK? There may be other options for him legally.”

Her muted remarks came as Washington and Islamabad, allies in the war on terror, struggle to repair ties that hit a low when US forces staged a secret raid into Pakistan that killed bin Laden in May last year.

They were strained to breaking point in November when US forces staged a botched raid that killed 24 Pakistani troops, prompting Islamabad to cut off the land route for supplies to Nato troops in neighboring Afghanistan.

Carl Levin and John McCain, the top senators from the two major US parties on the Senate Armed Services Committee, called Afridi's sentence “shocking and outrageous” and urged Pakistan to pardon and free him immediately.

“Dr. Afridi's continuing imprisonment and treatment as a criminal will only do further harm to US-Pakistani relations, including diminishing Congress's willingness to provide financial assistance to Pakistan,” they warned.