Yemeni forces clashed with Al Qaeda fighters Monday, leaving two militants believed to be behind threats to the U.S. dead, a security official told Reuters.
One militant was wounded and the fighting was still going on, the official said.
"These elements are believed to be behind the threats directed to the U.S. embassy," Reuters quoted the official as saying.
The Yemeni government ordered an "unprecedented" number of troops into a region controlled by a branch of Al Qaeda, as the U.S. and Britain, concerned about the threat of terrorism, both kept their embassies closed Monday in the capital of Sana.
The Obama administration increased the pressure on Islamic militants in Yemen Sunday after the Yemeni branch of Al Qaeda claimed responsibility for plotting the failed attempt to blow up Northwest Airlines Flight 253 on Christmas Day. The White House's top counterterrorism official didn't rule out U.S. military action.
Yemen deployed troops into provinces east of the capital to combat a growing Al Qaeda presence in the area, an aide to Yemeni President Ali Abdullah Saleh told The Wall Street Journal Sunday. The move, targeting the group identified as Al Qaeda in the Arabian Peninsula, or AQAP, follows pledges of increased U.S. and British aid to finance Yemen's effort to fight Islamic militants.
"The size of the convoy moving out of Sana was unprecedented," Eryani said. "The government wants to show the outside world that with proper help and support it can do the job needed to make Yemen safer than it is today."
Eryani said the troops are likely bound for the sweeping crescent of desert starting in provinces just east of Sana and stretching northeast along the Saudi border where U.S. and Yemeni officials say Al Qaeda's strength is growing.
The confrontation with Al Qaeda's offshoot in Yemen has gained new urgency since the 23-year-old Nigerian accused in the failed airline attack, Umar Farouk Abdulmutallab, told American investigators he received training and instructions from the group's operatives in Yemen. President Barack Obama said Saturday that the Al Qaeda offshoot was behind the attempt.
The White House counterterrorism chief John Brennan said the American Embassy, which was attacked twice in 2008, was shut Sunday because of an "active" Al Qaeda threat. A statement on the embassy's Web site announcing the closure cited "ongoing threats" from the terror group and did not say how long it would remain closed.
In London, Britain's Foreign Office said its embassy was closed for security reasons. It said officials would decide later whether to reopen it on Monday.
The closure comes as Washington is dramatically stepping up aid to Yemen to fight Al Qaeda, which has built up strongholds in remote parts of the impoverished, mountainous nation where government control outside the capital is weak.
Over the weekend, Gen. David Petraeus, the U.S. general who oversees the wars in Iraq and Afghanistan, announced that Washington this year will more than double the $67 million in counterterrorism aid that it provided Yemen in 2009. On Saturday, Petraeus met with Yemeni President Ali Abdullah Saleh to discuss coordination in the fight against Al Qaeda.
Britain announced Sunday that Washington and London will back the creation of a new counterterrorism police unit in Yemen. Britain will also host a high-level international conference Jan. 28 to hammer out an international strategy to counter radicalization in Yemen.
The U.S. also provided intelligence and other help to back two Yemeni air and ground assaults on Al Qaeda hideouts last month, reported to have killed more than 60 people. Yemeni authorities said more than 30 suspected militants were among the dead.
The U.S. has increasingly provided intelligence, surveillance and training to Yemeni forces during the past year, and has provided some firepower, a senior U.S. defense official has said. Some of that assistance may be through the expanded use of unmanned drones, and the U.S. is providing funding to Yemen for helicopters and other equipment. Officials, however, say there are no U.S. ground forces or fighter aircraft in Yemen.
On Thursday, the embassy sent a notice to Americans in Yemen urging them to be vigilant about security. and announced the increased counterterrorism aid.
Yemeni security officials said over the weekend that the country had deployed several hundred extra troops to Marib and Jouf, two mountainous eastern provinces that are Al Qaeda's main strongholds in the country and where Abdulmutallab may have visited. U.S. and Yemeni investigators have been trying to track Abdulmutallab's steps in Yemen, which he visited from August until Dec. 7. He was there ostensibly to study Arabic in San'a, but he disappeared for much of that time.
Al Qaeda has killed a number of top security officials in outlying provinces in recent months, underscoring Yemeni government's lack of control over the country. Tribes hold sway in the region, and many of them are discontented with the central government and have given refuge to Al Qaeda fighters, both Yemenis and other Arabs coming from Saudi Arabia or war zones in Iraq and Afghanistan.
Yemen, the ancestral homeland of Osama bin Laden and the site of the 2000 bombing of the USS Cole, has a weak central government whose authority does not extend far beyond the capital San'a. In addition to battling Al Qaeda fighters, it also faces two separate internal rebellions in the north and south.
Located at the tip of the Arabian peninsula, Yemen straddles a strategic maritime crossroads at the Red Sea and Gulf of Aden, the access point to the Suez Canal. Across the Gulf is Somalia, an even more tumultuous nation where the U.S. has said Al Qaeda militants have been increasing their activity. Yemen also borders Saudi Arabia, the world's leading oil producer.
There have been a spate of assaults on the U.S. Embassy in Yemen and it has closed several times over past threats.
In April, embassy personnel were put on a one-week lockdown, barred from leaving their homes or the embassy after Al Qaeda suicide bombings that targeted South Korean visitors.
In an attack in September 2008, gunmen and two vehicles packed with explosives attacked the U.S. Embassy, killing 19 people including an 18-year-old American woman and six militants. None of those killed or wounded were U.S. diplomats or embassy employees. Al Qaeda in Yemen claimed responsibility.
In March 2003, two people were shot dead and dozens more are wounded as police clash with demonstrators trying to storm the embassy. In March 2008, three mortars missed the U.S. Embassy and crashed into a high school for girls nearby, killing a security guard
Last January, gunmen in a car exchanged fire with police at a checkpoint near the embassy, hours after the embassy received threats of a possible attack by Al Qaeda. Nobody was injured.
As recently as July, security was upgraded in San'a after intelligence reports warned of attacks planned against the U.S. Embassy.
The Wall Street Journal and Associated Press contributed to this report.