U.S. Defense Department on Monday called the terror group al-Qaeda in the Arabian Peninsula a serious threat in Yemen and around the world.

"It's a serious threat, and it's a threat not only to Yemen, but the U.S. and other regional interests," Pentagon spokesman Bryan Whitman said.

The failed terror plot, in which two suspicious packages were found last week on cargo planes originated from Yemen and destined for the United States, has spurred security scare across the Atlantic.

Top U.S. officials are increasingly confident that al-Qaeda Yemeni affiliate was behind the plot, even though they stressed investigation is still underway and no final conclusion can be drawn at this point.

Officials of the Defense Department have been working with Yemen to implement "a holistic approach" to address security and counterterrorism concerns in the nation, Whitman said.

But the department is not considering any overt move in Yemen, he added. The United States has a modest training mission in the country, and works with the Yemeni military to build capabilities to counter al-Qaeda in the Arabian Peninsula.

"We work very closely with the government of Yemen on our counterterrorism assistance activities," he said.