The United Nations is very concerned about the health of an American U.N. official kidnapped in Pakistan last month and wants him released as soon as possible, a spokeswoman said on Tuesday.

Kidnappers holding the official with the U.N. refugee agency, John Solecki, said he was seriously ill with a cardiac problem and authorities should act on their demands to release prisoners.

We are very concerned that his health condition is deteriorating and we would really like him to be released as soon as possible, said Jennifer Pagonis, a U.N. spokeswoman in Islamabad.

Solecki, 49, head of the U.N. High Commissioner for Refugees (UNHCR) office in Baluchistan province, was kidnapped in the provincial capital, Quetta, on February 2 when gunmen ambushed his car and shot dead his driver.

Militants from a previously unknown group said they had kidnapped him and made various demands, including the release of prisoners it said were being held by the government.

Separatist militants have for decades fought a low-intensity insurgency in Baluchistan for control of the province's gas and other resources.

A spokesman for the group, the Baluchistan Liberation United Front (BLUF), telephoned a Pakistani news agency late on Monday and said Solecki was seriously ill with a cardiac problem.

We are providing him all possible medical treatment but his condition is not improving, the Online news agency cited the spokesman as saying.

The BLUF spokesman, Shahiq Baluch, said they were giving two more days for the acceptance of their demand for the release of more than 1,000 prisoners, after which they would not be responsible for Solecki.

If something happens to him, BLUF will not be responsible. The United Nation will be fully responsible for the consequences, the news agency quoted the spokesman as saying.

The spokesman said the United Nations was not serious about the group's demands.

The BLUF had earlier demanded U.N. intervention to secure release of 141 women it said were held in government torture cells, information on more than 6,000 missing people and resolution of issue of Baluch independence under the Geneva Convention.

(Additional reporting and writing by Augustine Anthony; Editing by Robert Birsel)