NEW DELHI: India's relations with archrival Pakistan "cannot be business as usual" in the wake of a spate of attacks in Kashmir, Prime Minister Manmohan Singh said Tuesday in a statement that threatens to ratchet up tensions in the wake of the Himalayan violence.

A series of tit-for-tat attacks - including the beheading of an Indian soldier - across the so-called Line of Control that divides the Himalayan region has killed two Pakistani and two Indian soldiers.

"What has happened is unacceptable," Prime Minister Manmohan Singh said of the killing of the two Indians, according to Indian media reports. He made the brief comments to reporters at a New Delhi gathering for India's annual day honoring the military.

India and Pakistan have been rivals for decades, though ties had been improving markedly in recent years. The two have fought three wars since they were carved out of British India in 1947 - two of them over Kashmir. The region is divided between the two countries, but each claims it in its entirety.

While the peace process ground to a halt after the 2008 Mumbai terror attack by Pakistani gunmen, who New Delhi has said were supported by Pakistan's powerful intelligence agency, the two countries have since then worked to mend their diplomatic ties.

The Kashmir fighting, the worst in the region in years, began Jan. 6 when Pakistan accused Indian troops of raiding an army post and killing a soldier. India denied launching the attack and said its troops had fired across the border in response to Pakistani shelling that had destroyed an Indian home.

Two days later, India said Pakistani soldiers, taking advantage of heavy fog, crossed the de facto border and killed two Indian soldiers, beheading one. On Jan. 10, Pakistan said Indian troops had fired across the border and killed another of its soldiers. The Pakistani army said the shooting was unprovoked, while the Indian military said its troops were responding to fire from across the frontier.

Pakistan denies India's allegations and has suggested U.N. monitors in the region conduct an inquiry - a call that India rejected, saying it didn't want to internationalize the issue.

Pakistan and India struck a cease-fire agreement over Kashmir in November 2003. There have been periodic violations of the cease-fire, but the incidents during the past week have been the most serious.