U.S. President Barack Obama raises concerns about the threat in Yemen after a suicide bomber in army uniform kills more than 90 soldiers in the heart of the Yemeni capital Monday.

An al Qaeda affiliate threatened more strikes if a U.S.-backed campaign against militants in the front-line state

did not stop.

(SOUNDBITE) (English) U.S. PRESIDENT BARACK OBAMA SAYING:

"We are very concerned about al Qaeda activity and extremist activity in Yemen. A positive development has been a relatively peaceful transition in Yemen,. and we participated diplomatically along with Yemen's neighbors in helping to leads to a political transition, but the work is not yet done."

The attack, which also wounded more than 200 people, underscored the threat Yemen faces in its fight to dislodge Islamist militants entrenched in the south and threatening vital shipping lanes in the Gulf of Aden.

The United States is increasing its military support for Yemen's government and the U.S. military has itself targeted militants in Yemen using drones, which have frequently killed civilians and are deeply resented

(SOUNDBITE) (English) U.S. PRESIDENT BARACK OBAMA SAYING:

"I think one of the things we have learned from the Afghanistan experience is for us to stay focused on the counter terrorism issue to work with the government, to not over extend ourselves to operate smartly."

Monday's attack, along with an ambush on Sunday on a U.S. military training team, indicated their campaign could be entering a dangerous new stage in Yemen, which borders oil giant Saudi Arabia

Deborah Lutterbeck, Reuters