The United States stressed on Saturday that it stands ready to assist Yemen in its fight against al-Qaeda in the Arabian Peninsula following a failed parcel bomb plot against synagogues in Chicago a day earlier.

John Brennan, U.S. President Barack Obama's top advisor for homeland security and counter-terrorism, spoke to Yemeni President Ali Abdallah Saleh and underscored the "importance of close counterterrorism cooperation, including the need to work together on the ongoing investigation into the events over the past few days," the White House said.

Brennan emphasized that "the United States stands ready to assist the Yemeni government and the Yemeni people in their fight against al-Qaeda in the Arabian Peninsula."

Two explosives-filled parcels from Yemen, bound for synagogues in Chicago, were intercepted Friday respectively on cargo planes in Dubai and at Britain's East Midlands Airport on a tip-off from Saudi Arabia authorities.

British Home Secretary Theresa May confirmed Saturday that the device was viable and could have exploded. She said "the target may have been an aircraft and had it detonated the aircraft could have been brought down."

The plot came four days ahead of U.S. congressional mid-term elections. In his speech Friday at the White House, Obama said: " We know that al-Qaeda in the Arabian peninsula, the terrorist group based in Yemen, continues to plan attacks against our homeland, our citizens, and our friends and allies. Going forward, we will continue to strengthen our cooperation with the Yemeni government to disrupt the plotting and to destroy the al-Qaeda affiliate."

Obama on Saturday spoke to British Prime Minister David Cameron about the plot and they agreed to work together to prevent and disrupt future efforts to attack citizens in both countries.

A Yemeni security official said initial investigation showed that the Yemen-based al-Qaeda in the Arabian Peninsula was behind the botched parcel bomb plot against the United States.

With an intelligence help by the United States, Yemen has beefed up security campaign including air raids on al-Qaeda wing since the Yemen-based wing claimed credit for a December failed plot to blow up a U.S. passenger plane.

In his call to President Saleh, Brennan lauded "the courageous efforts" of Yemeni security forces, saying they are battling al- Qaeda terrorists on a regular basis. He said that Yemen's international partners, including Britain and Saudi Arabia, stand ready to assist the Yemeni people in "developing a more stable and prosperous Yemen that will undermine al-Qaeda's efforts in Yemen."