Pakistani Prime Minister Yousaf Raza Gilani said on Friday the situation on the Indian border was fragile as US vice president-elect Joe Biden arrived for talks aimed at easing strained ties between the South Asian neighbours.
Tension between nuclear-armed Pakistan and India surged after coordinated attacks by 10 terrorists on of Mumbai in late November that killed 179 people.
India blamed Pakistani militants from the outset, but Indian Prime Minister Manmohan Singh said for the first time this week the assault must have had the support of "some official agencies" in Pakistan.
Pakistan has denied involvement by state agencies and rejected Singh's accusation, saying he was ratcheting up tension. It confirmed on Wednesday the lone surviving gunman from the attack was Pakistani.
"The situation on our eastern border has once again become very fragile," Gilani told a seminar in Islamabad.
Gilani said it was regrettable that India had frozen a four-year-old peace process that had brought better ties between the rivals who have fought three wars since 1947.
"The world must not let tension between India and Pakistan escalate," he said.
Biden, outgoing chairman of the US Senate Foreign Relations Committee, arrived in Pakistan with Senator Lindsey Graham of the US Armed Services Committee, a US embassy spokesman said.
He was due to meet President Asif Ali Zardari and other leaders.
While tension has been high, there has been no sign of a repeat of a 2002 troop build-up which followed an attack in New Delhi that India also blamed on Pakistani-based militants.
Analysts say the chances of India resorting to military action have receded.
"Irrational, deadly actors"
Pakistani officials have warned that if there was a risk of conflict with India it would move forces from its western border with Afghanistan, where they are fighting Taliban and Al-Qaeda militants.
That would undermine a US plan to almost double the number of its troops in Afghanistan as part of a surge to quell an intensified Taliban insurgency.
Dell Dailey, the State Department's counter terrorism coordinator, told reporters in Washington on Tuesday the United States had not seen any move of Pakistanis forces from the western border "in any degree that's measurable".
The tension with India has also had ramifications on Pakistani domestic politics with Gilani sacking his national security adviser on Wednesday for releasing news of the nationality of the surviving gunman before consulting him.
"The incident demonstrates just how fragile Pakistan's internal political situation remains," Lisa Curtis, a research fellow at the Heritage Foundation, said in a note.
The military's years of support for militants fighting in Afghanistan and India was costing Pakistan dearly, she said.
"Islamabad's foreign and domestic policies have become hostage to the agenda of these irrational, deadly actors who also increasingly target Pakistani institutions," she said.
Curtis said it would be a grave error for Pakistan to fail to punish those responsible for the Mumbai attack on the excuse that would appear to be succumbing to Indian pressure.
Indian Home Minister Palaniappan Chidambaram said on Wednesday he was not going to the United States to present evidence gleaned from the Mumbai attacks, partly because of Pakistan's confirmation the surviving gunman was Pakistani.