DUBAI (Reuters) -Houthi security forces have detained 11 United Nations personnel in Yemen over the past three days and the U.N. is seeking their safe and unconditional release as soon as possible, U.N. spokesperson Stephane Dujarric said on Friday.

He said the U.N. was very concerned about the developments and was seeking clarification from the Houthis about why the Yemeni staff were detained. The two women and nine men work for five different U.N. agencies and the U.N. envoy for Yemen.

“We’re pursuing all available channels to secure the safe and unconditional release of all of them as rapidly as possible,” said Dujarric, adding that the U.N. also wanted access to the staff.

In a series of raids, armed Houthi intelligence officers detained at least nine U.N. employees, three employees of the U.S.-funded pro-democracy group National Democratic Institute (NDI) and three employees of a local human rights group, three officials of Yemen’s internationally recognised government told Reuters on Friday.

Intelligence officers of the Houthi group, which controls the capital Sanaa and large parts of the north of the country, raided the homes and offices of these people, confiscating phones and computers.

The internationally recognised government controls mostly southern parts of Yemen.

The NDI did not immediately respond to a Reuters request for confirmation or comment. A Houthi spokesperson did not immediately comment.

The Houthis, who are aligned to Iran, have attacked shipping in the Red Sea, drawing airstrikes from the United States and Britain. They have held around 20 Yemeni employees of the U.S. embassy in Sanaa for the past three years. The embassy suspended operations in 2014.

(Reporting by Mohammed Ghobari, Andrew Mills and Michelle Nichols; Editing by Peter Graff and Timothy Heritage)