International media watchdogs urged Pakistan on Tuesday to investigate the disappearance of a journalist working for the British Broadcasting Corporation.
The journalist, Dilawar Khan Wazir, works for the BBC's Urdu-language service in the troubled tribal areas on the Afghan border, where security forces have been battling Islamist militants linked to Al-Qaeda and the Taliban.
The press is generally free in Pakistan but several reporters covering the conflict in the tribal areas have been abducted and some have been killed over recent years.
Wazir, who also reports for Pakistan's Dawn newspaper, went missing in suspicious circumstances after visiting his brother in Islamabad on Monday.
"The Pakistani authorities must do their utmost to shed light on the disappearance of Dilawar Khan," Paris-based Reporters Without Borders said in a statement.
"The circumstances of his disappearance lead us to fear he was abducted."
Fears for Wazir were raised after a group of unidentified men visited a university hostel where his brother lives and said Wazir had been hurt in an accident and taken to a hospital.
The brother, Zulfiqar Ali, and the BBC checked at the hospital but there were no signs of Wazir.
Last year, a prominent journalist in the region, Hayatullah Khan, was abducted after reporting that an Al-Qaeda leader had been killed by a US missile.
That contradicted the government, which said the militant had been killed when explosives stored at his hideout exploded.
In June, Khan's body was found dumped. He appeared to have been kept in captivity and killed shortly before he was found. Reporters' groups said it looked as if he had been held by security agents.
The New York-based Committee to Protect Journalists also expressed concern about Wazir and called for action.
"A number of journalists have disappeared in Pakistan for days or months at a time," the group's executive director, Joel Simon, said in a statement.
"The government must act swiftly to find Dilawar Khan or, if he is being held by government agents, to disclose his whereabouts and the basis for his detention," he said.
The BBC said it was seriously concerned and the director of its World Service, Nigel Chapman, had written to the Interior Ministry requesting urgent help.
"We expect them to do their utmost in helping us trace our reporter," the BBC said in a statement.
There has been no official word on Wazir's disappearance.
The BBC said earlier the military and Information Ministry referred queries to the Interior Ministry. Interior Ministry officials were not immediately available for comment.
Wazir is from the South Waziristan region but moved to the nearby town of Dera Ismail Khan last year after security deteriorated in South Waziristan.
In August, Wazir's 15-year-old brother was abducted and later found near the family home in South Waziristan with head wounds. He later died.