NEW DELHI, India - In signs of growing regional tension since last month's Mumbai attacks, Pakistan scrambled fighter jets over several of its cities yesterday, and India's foreign minister told Indian diplomats in New Delhi that the country is keeping all its options open to bring the perpetrators of the attacks to justice.

"We have so far acted with utmost restraint," Foreign Minister Pranab Mukherjee told the more than 120 envoys from posts around the world, according to news reports. But "we will take all measures necessary as we deem fit to deal with the situation."

A senior government official later called Mukherjee's tough talk "an expression of political will that India will not take this lying down." He added that the option of "precision air strikes" on terrorist training camps in Pakistan would remain on the table if Islamabad did not act effectively against groups fomenting terrorism against India.

Pakistan has denied involvement in the Mumbai attacks, which killed more than 160 people and wounded 230.

Yesterday, Pakistan put its air force on high alert, with several fighter jets conducting exercises over the capital of Islamabad, as well as Rawalpindi, Lahore and Pakistan-controlled Kashmir. Offices of newspapers and TV channels were inundated with calls from people asking whether the exercises were a response to air strikes by India.

A Pakistani air force spokesman, Commodore Humayun Viqar, said in a statement, "In view of the current environment, PAF has enhanced its vigilance."

The action coincided with the arrival in Islamabad of Adm. Michael Mullen, the Joint Chiefs of Staff chairman. He met with Pakistan's army chief, Gen. Ashfaq Kiyani, and Lt. Gen. Ahmed Shuja Pasha, head of its Inter-Services Intelligence agency.

Mullen thanked both men for their efforts, and that of the Pakistani government, to arrest members of the outlawed Islamist group Lashkar-e-Taiba and other extremist groups suspected of involvement in the attacks, said his spokesman, Navy Capt. John Kirby.

A Pakistani official who spoke on the condition of anonymity said Kiyani told Mullen that Pakistan was trying its best to defuse tension with India but that "any aggression will be matched by a befitting response."

Pakistan's government has offered to help in the investigation of the Mumbai attacks but has said that India has not shared any hard evidence about the alleged involvement of Pakistani citizens.

Yesterday, however, India's Ministry of External Affairs handed over to Pakistan's acting high commissioner in New Delhi a letter that it said was written by the only surviving Mumbai gunman, Mohammed Ajmal Kasab. In the letter, Kasab said he and the nine other gunmen who died in the three-day Mumbai siege "were from Pakistan and has sought a meeting with the Pakistan High Commission," the ministry said.