Fighting between government forces and Tamil insurgents in Sri Lanka's north and east and a suicide bombing in the capital left dozens dead, including youths killed in what the rebels alleged was an air raid on a home for teenagers, officials said.

The clashes along the frontiers dividing government and rebel territory in the north and east, and the blast in Colombo appeared to dash what little hope was left for a quick end to fighting that has steadily worsened over the past four weeks, undermining an already shaky cease-fire.

The 2002 truce was intended to halt more than two decades of bloodshed between the government, dominated by Sri Lanka's 14 million Sinhalese, and the rebels, who have been fighting since 1983 for an independent homeland for the country's 3.2 million Tamils.

CountryWatch: Sri Lanka

While it remains officially in effect, months of shootings and bombings already had left it in tatters before the latest round of clashes.

U.N. Secretary-General Kofi Annan was "increasingly alarmed" over the violence and called on both sides "to cease hostilities immediately and to return to the negotiating table," U.N. spokesman Stephane Dujarric said at U.N. headquarters in New York.

In fighting Monday, Sri Lankan air force jets bombed the northeastern Mullaitivu district, deep inside rebel territory.

The pro-rebel TamilNet Web site, citing officials from the Liberation Tigers of Tamil Eelam, reported that 61 girls who were studying there were killed and another 60 were injured.

However, Air Force spokesman Group Capt. Ajantha Silva said the military had proof that the site was a rebel base.

An official from a Nordic cease-fire monitoring team, speaking on condition of anonymity because of the sensitivity of the information, said the site appeared to be a home for students between 17 and 20 years old.

The official said a monitor who visited the site saw only 19 bodies at a nearby hospital, but believed there may have been more elsewhere.

Hours later in Colombo, a suicide bomber in an auto rickshaw blew himself up as a car carrying Pakistan's high commissioner, Basir Ali Mohmand, passed along a crowded road. At least seven people were killed, including four army commandos guarding the envoy, the government said. Another 10 people were wounded in the bombing less than a mile from the residence of President Mahinda Rajapakse.

But the diplomat, who was believed to be the target of the blast, escaped unhurt, he said, blaming the Tigers for the attack. Pakistan is a major supplier of arms to Sri Lanka's military.

Tamil Tiger officials were not immediately available to comment, although in recent months they have often kept quiet after such attacks, neither confirming nor denying involvement.

Pakistani officials said it was the first attack on any of their diplomats in Sri Lanka.

A day earlier, at least 15 people died in fighting around the St. Philip Neri Church in Allaiiddy, a predominantly Tamil village located on an island just west of the Jaffna Peninsula. The island, like the peninsula, is held by the government.