|The row over Davis' possible diplomatic immunity has sparked widespread protests across Pakistan [AFP]
Raymond Davis, a CIA employee accused of murdering two Pakistanis in the country's eastern city of Lahore, has appeared handcuffed in court there.
The 36-year-old former US special forces soldier refused to sign a charge sheet against him, claiming diplomatic immunity, officials said on Friday.
Davis' detention has severely frayed ties between Washington and Islamabad, with US politicians threatening to cut aid to the country, while the Pakistani leadership has been forced to contend with immense domestic pressure to prosecute Davis in Pakistan.
The US insists that Davis is immune from prosecution because he is listed as a US embassy staff member.
Davis has said that he shot the two Pakistanis in self defence, claiming that they tried to rob him on a Lahore street on January 27 this year.
US security officials have confirmed on condition of anonymity that Davis worked as a security contractor with the CIA. He was deployed to Pakistan under diplomatic cover, they said.
Washington says that Davis' exact job is not relevant to the debate of whether or not he enjoys immunity from prosecution.
Pakistani officials continue to deliberate over whether or not Davis enjoys diplomatic immunity, but face pressure from a population where anti-US sentiment is widespread and calls for him not to be allowed to leave the country.
During Friday's hearing, which was held in a Lahore jail behind closed doors, prosecutors attempted to present Davis with a charge sheet.
More than 300 armed police officers guarded the Kot Lakhpat jail, where the hearing took place.
The judge also asked Davis if he had engaged a defence lawyer, according to Asad Manzoor Butt, a lawyer for a Pakistani bystander who was killed when a US vehicle rushed to assist Davis after the shootings.
Davis, however, refused to sign the charge sheet and insisted that he would not participate in the case because he has immunity from prosecution, Butt said.
The question of whether Davis has immunity is currently also being considered by the Lahore High Court. The next date of hearing in that case is March 14.
Abdus Samad, the prosecutor in the case, said Davis would be formally charged on March 3, the date of the next hearing.
Police have said they recovered a Glock pistol, four loaded magazines, a GPS navigation system and a small telescope from Davis' car after the shooting.
While the US embassy declined comment, a spokesperson confirmed that representatives of the US consulate in Lahore were present at the hearing.
Meanwhile, police in northwest Pakistan said they had arrested a US citizen who was staying in the area on an expired visa on Friday.
The man was detained in Peshawar, the capital of Khyber-Pakhtunkhwa province, Haroon Khan, a police officer, told the Associated Press news agency.
Khan identified the man as Aaron Mark DeHaven from the state of West Virginia in the US. The US embassy said that it was looking into the case.