The Yemeni officials say two suspects were killed in fighting outside the capital, Sana'a.

Authorities have stepped up security around Sana'a and its airport. Foreign embassies are asking their citizens in Yemen to be on alert.

The United States is investigating the ties between Yemeni militants and the man accused of trying to blow up an airplane in the United States on Christmas Day. The Nigerian suspect says he received training from the al-Qaida affiliate in Yemen.

The United States says it will double its aid to Yemen this year, giving it $140 million to counter al-Qaida as the government fights a rebellion in the north and a secessionist movement in the south.

American Institute for Yemeni Studies resident director Stephen Steinbeiser is concerned about how the money will be spent, noting that Yemen's problems have been brewing for years.

"I am not sure that giving even huge amounts of money at this point will make a significant difference especially because, if the money is given just for military purposes, I don't see a military solution to these problems," he said. "I think that it is true that the problems are symptomatic of social issues and economic issues which the country has been grappling with for a number of years and really needs help developing programs."

The Sana'a-based institute director says alienation is particularly a problem with Yemenis returning from years in the American military prison at Guantanamo Bay where they were held as terror suspects.

"I think that it would be very easy for prisoners who are held in Guantanamo Bay, detainees, to return to the country and to be very angry and look for western targets and particularly American targets," he added. "The government does not seem to have a full rehabilitation program in effect."

It is not clear if some of the foreign aid will go to more comprehensive rehabilitation projects. Britain plans to hold an international conference on improving the security situation in Yemen later this month.

Related stories:

White House: Al-Qaida threat closes US embassy in Yemen

Bin Laden relatives found living in Iran

美稱拉登仍在活動 擬繼續追捕

Bin Laden 'still spends time in Afghanistan'

（來源：VOA 編輯：陳丹妮）