ISLAMABAD - Pakistan will not be the first to act in any face-off with India but is prepared to defend itself from aggression, Prime Minister Yousaf Raza Gilani said on Saturday.

Relations between the nuclear-armed rivals have deteriorated sharply after India blamed Islamist militants based in Pakistan for the last month's attacks on Mumbai that killed 179 people.

In a sign of mounting tension, Pakistan has canceled army leave and shifted some troops from its western border with Afghanistan to the eastern border with India.

That is likely to cause alarm in the United States which does not want to see Pakistan distracted from the battle against al Qaeda and Taliban militants on the Afghan border.

The United States has urged both sides to refrain from further raising tension. China and Iran have also tried to calm things down.

Gilani said Pakistan did not want war but was ready for one.

"Our friends are trying their best to persuade India so as to avoid aggression ... to avoid any sort of misadventure," he told Muslim diplomats at a ceremony to mark the anniversary of the murder of former prime minister Benazir Bhutto.

"But at the same time, our armed forces are highly professional. They are fully prepared but at the same time I assure you, once again, that we will not act. We will only react," Gilani said.

India, the United States and Britain have blamed the Mumbai attack on Pakistan-based Islamist group Lashkar-e-Taiba, set up to fight Indian rule in the disputed Kashmir region.

Pakistan has condemned the attacks and has denied any state role, blaming "non-state actors." It has offered to cooperate with India but denies Indian claims that it has been handed firm evidence of links to militants in Pakistan.

Travel warning

As Pakistan canceled army leave and moved some troops from the western border with Afghanistan to the eastern frontier with India, the foreign ministry in New Delhi warned Indian citizens it would be unsafe to travel to, or be in, Pakistan.

A bus service linking the Indian capital and the Pakistani city of Lahore was still running on Saturday despite the warning, local media said.

The South Asian neighbors both tested nuclear weapons in 1998. They have fought three wars since independence from Britain in 1947 and came to the brink of a fourth after gunmen attacked the Indian parliament in December 2001.

Although many analysts say war is very unlikely, international unease is growing.

"I think it's more brittle perhaps but I don't know that it's actually going to translate into a war," said Indian strategic security analyst C. Uday Bhaskar.

"The point that India is trying to make is that we do not in any way threaten the territorial integrity of Pakistan," he said.

He said India's travel warning should be seen in a limited context and that no confirmed troop movements had been observed in India.

"India does have the capacity to respond but I still don't see this as a sign of limited war or a conventional war," he said.

Pakistan media reported that "several" Indian nationals had been held in the last two days after a bombings in the Pakistani city of Lahore.

Earlier, Indian police said they had arrested three militants, including a Pakistani soldier, for allegedly plotting a suicide attack in Indian-administered Kashmir.

Pakistan denied that the arrested man was a serving soldier.

On Friday, Indian Prime Minister Manmohan Singh discussed the tension with Pakistan during a scheduled meeting with chiefs of the army, navy and air force, his office said.

Indian media continued its blanket coverage of the crisis, with the Hindustan Times newspaper running a front-page headline: "Pak army on the march."

"Whipping up war hysteria is Pakistan's way of deflecting attention from its responsibility to act against the perpetrators of 26/11 or to address informed concerns that there may have been institutional support for the terrorists," The Indian Express said in an editorial, referring to the Mumbai attacks.