The British Embassy in Yemen's capital closed and evacuated its staff early Wednesday, authorities said, the latest diplomatic post to shut down in the Arab world's poorest country amid turmoil following Shiite rebels seizing power.

In a statement, U.K. Minister for the Middle East Tobias Ellwood also urged British citizens still in Yemen to "leave immediately." This comes as the State Department confirmed it also closed the U.S. Embassy in Sanaa and evacuated its staff because of the political crisis there and security concerns.

"The security situation in Yemen has continued to deteriorate over recent days," Ellwood said. "Regrettably we now judge that our embassy staff and premises are at increased risk."

Yemen has been in crisis for months, with Shiite Houthi rebels besieging the capital and then taking control. Earlier Tuesday, U.S. officials said the embassy closure would not affect counterterrorism operations against al-Qaida's Yemen branch, which America views as the world's most dangerous branch of the terror group.

The United Nations has been trying to broker talks between the Houthis and others in Yemen since the Shiite rebels dissolved parliament after earlier besieging the country's president, who later resigned while armed militants surrounded his home.

Abdel-Malek al-Houthi, who leads the Shiite rebels, warned his enemies Tuesday not to stand in his hard-line movement's way and denounced foreign governments for removing their diplomats.

"We will not accept pressures. They are of no use," al-Houthi said in speech broadcast on the rebel group's own al-Masirah satellite television network. "Whoever harms the interest of this country could see that their interests in this country are also harmed."

Al-Houthi made a series of similarly threatening but vague remarks, and offered no explanation for what specific retaliatory action he might have in mind.

The Houthis, who are traditionally based in northern Yemen bordering Saudi Arabia, swept into Sanaa in September and have seized other territory since. Many link the Houthis to regional Shiite power Iran, though the rebels deny they are backed by the Islamic Republic.