SHANGHAI: Al Qaeda Still Greatest Threat to US: Barack Obama, US President Barack Obama on Monday called al Qaeda the biggest threat to US security, as his aides stepped up pressure on Afghanistan and Pakistan to cooperate with Washington’s strategy in the troubled region.

Obama, who was visiting Shanghai as part of a nine-day Asian tour, is nearing a decision on whether to send up to 40,000 more troops to fight the eight-year-old war in Afghanistan.

He has faced criticism at home for “dithering” on the Afghan war strategy, and the political pressure has been rising to make a decision soon.

“I continue to believe that the greatest threat to the United States’ security are the terrorist networks like al Qaeda,” Obama told Chinese students at a town hall meeting in Shanghai.

“They have now moved over the border of Afghanistan and are in Pakistan, but they continue to have networks with other extremist organizations in that region and I do believe it is important for us to stabilize Afghanistan.”

One of Obama’s top aides had delivered a letter to Pakistani President Asif Ali Zardari urging him to work with the United States against extremists, the New York Times reported on Monday.

In the letter, Obama offered Zardari a range of new incentives to the Pakistanis for their cooperation, including enhanced intelligence sharing and military cooperation, according to the Times, which said the missive was delivered in person by National Security Adviser General James Jones.

Jones’s press secretary, Mike Hammer, confirmed that Jones had traveled to Pakistan just before joining Obama over the weekend in Singapore for a summit of Asia Pacific leaders.

In addition to Zardari, Jones met with Pakistani Prime Minister Yusuf Raza Gilani, Army chief General Ashfaq Kayani and other officials.

But Hammer would not discuss what was said in the meetings nor whether a letter was delivered.

The effort to seek greater cooperation from Pakistan came as Secretary of State Hillary Clinton called on Afghan President Hamid Karzai to do a better job of tackling corruption within his government and create a major crimes tribunal.

“We’re going to be doing what we can to create an atmosphere in which the blood and treasure that the United States has committed to Afghanistan can be justified and can produce the kind of results that we’re looking for.

“Now, we believe that President Karzai and his government can do better. We’ve delivered that message,” she added.