Gunmen in Yemen kidnapped on Tuesday four aid workers -- a Colombian, a German, an Iraqi and a Palestinian -- along with their two Yemeni drivers, state news agency Saba said.
"An armed group in Wadi Ahjar," 50 km northwest of Sanaa in the province of Mahwit, "kidnapped six employees" of an international aid agency, Saba reported.
A UN employee in Sanaa confirmed, saying the six work for the office for the coordination of humanitarian affairs (OCHA).
The Iraqi and the Palestinian are women.
They were kidnapped as they were returning to Sanaa from a "displaced persons' camp in the town of Hard, in (the northern) Hajja province," Saba quoted local official in Mahwit Ali Al Zaikam as saying.
"Security forces have besieged the area the group is held in and have reached them by telephone. They are in very good condition," Zaikam said.
The abductors are calling for the release of "Ali Ghanem Al Zubairi, held at the central prison in Sanaa over criminal charges," reported Saba.
"Tribal dignitaries in the region are negotiating their release," Zaikam said.
The German foreign ministry confirmed that it is aware of the kidnapping.
Crisis units in Berlin and at the German embassy in Sanaa are making all efforts to clarify the situation, a spokeswoman said, adding that all the relevant authorities were cooperating closely in the matter.
Yemen's powerful tribes often kidnap foreigners for use as bargaining chips with the authorities. More than 200 foreigners have been abducted over the past 15 years. Almost all were later freed unharmed.
The latest was Norwegian United Nations Development Programme employee Gert Danielsen, who was snatched from Sanaa on January 14 by armed men aiming to pressure the government to release members of their tribe held for killing four soldiers.
He was freed on Friday. A tribal source said his release came after the captors received "tribal guarantees to answer their demand" for the freeing of a relative jailed on a criminal conviction.