President Barack Obama has sent his National Security Adviser Gen (rtd) James Jones and CIA chief Leon Panetta to express his concerns to Islamabad, the book entitled 'Obama's War' said.

Obama, via his officials, also slammed Pakistan President Asif Ali Zardari for not adequately interrogating LeT commander Zakiur Rehman Lakhvi in 26/11 Mumbai attacks case and said "he continues to direct LeT operations from his detention center." But the US officials returned with nothing after powerful Army chief Gen Ashfaq Parvez Kayani refused to adhere to any of the four demands made by them. Kiyani had other concerns -- India, the book says.

"The President wants everyone in Pakistan to understand if such an attack connected to a Pakistani group is successful there are some things even he would not be able to stop. Just there are political realities in Pakistan, there are realities in the US", an investigative US journalist Bob Woodward noted the officials' message to Zardari in the book.

"No one will be able to stop the response and consequences. There is not a threat, just a statement of political fact." According to US intelligence, LeT is threatening attacks in the US and the possibility of such an act is rising each day, Jones was quoted as saying in the book.

After meeting Zardari, US officials met Kayani and Jones told the Army Chief that it is time to act on the requests all the four requests made by Obama but he "would not budge very much". Kayani said, "I’ll be the first to admit, I’m India centric".

Woodward wrote that Jones and Panetta left feeling they had made only baby steps. "How can you fight a war and safe havens across the border?" Panetta asked in frustration. The latest intelligence showed trucks crossing the border that were full of Taliban combatants with all kinds of weapons packed in the back.  They were being waved through into Afghanistan to kill Americans at checkpoints controlled by the Pakistanis.

"It's a crazy kind of war," Panetta said. According to the award winning author, Pakistan has repeatedly refused to accept US request to share names of all airline passengers travelling to or from Pakistan on the grounds that such a disclosure would violate their sovereignty.

"They also suspected it would give the US insight into where their intelligence officers were going. Most ISI agents were flying east to India or Bangladesh, so the US had proposed just getting data on flights heading west to the Persian Gulf, Europe and the United States. "But the Pakistanis has stubbornly resisted," Woodward wrote.

In the event of a terrorist attack, the Obama officials were worried that it would be hard for Obama to defend Pakistan because their leaders had refused to do what had been easy, especially on the visas and passengers lists, he wrote further.