Several international aid organisations have suspended their operations in the Pakistani province of Balochistan, following threats of suicide attacks.
Pakistani police have stepped up security for aid agencies
A number of foreign aid workers have taken shelter in hotels, police said.
Groups which have temporarily halted work include the United Nations refugee agency and the aid organisation, Medicines San Frontieres.
Militants are believed to be hiding in border areas of Pakistan since being driven from Afghanistan in 2001.
A Pakistani government agency responsible for security at
refugee camps alerted the aid agencies to the threat of possible attacks.
The UN High Commissioner for Refugees (UNHCR) said it was taking the threat seriously.
"We have suspended our operation and shifted about a dozen foreign staff members to hotels or other safer places," spokesman Babar Baluch told AFP news agency.
Provincial police chief Yaqub Chaudhry said security had been increased in the city of Quetta and other parts of the province.
Forces have been deployed at the offices used by the aid agencies, and foreign aid workers have been asked to inform the police about their movements.
An official of the aid agency, Medicines Sans Frontiers (MSF) said that they have closed their offices and would meet on Wednesday to decide the future strategy.
MSF has suspended operations in Afghanistan after five of its workers were killed in an ambush on Wednesday.