The Sri Lankan government today formally declared an end to the 25-year civil war after the army took control of the entire island and killed the leader of the Tamil Tigers.

Sri Lankan President Mahinda Rajapaksa this morning delivered a victory address to parliament, declaring that his country had been "liberated" from terrorism.

Recounting how the rebels, known formally as the Liberation Tigers of Tamil Eelam, (LTTE) once controlled a wide swathe of the north and much of the east, Rajapaksa said that for the first time in 30 years, the country was unified under its elected government.

"We have liberated the whole country from LTTE terrorism," he said, declaring Wednesday a national holiday to celebrate the armed forces.

Addressing parliament in the Tamil language, Rajapaksa said the war was not waged against the Tamil people.

"Our intention was to save the Tamil people from the cruel grip of the LTTE. We all must now live as equals in this free country," he said.

"We must find a homegrown solution to this conflict. That solution should be acceptable to all the communities. We have to find a solution based on the philosophy of Buddhism."

According to the Sri Lankan army, the chief of the LTTE, Velupillai Prabhakaran, was shot dead by Sri Lankan forces.

There were differing accounts of how he met his end. According to one version he was shot while trying to flee the war zone in an ambulance after the final battle in an offensive that has killed thousands of Tamil civilians since January.

But the Associated Press reported that he and his top deputies drove an armour-plated van accompanied by a bus filled with rebel fighters toward approaching Sri Lankan forces, sparking a two-hour firefight. Troops eventually fired a rocket at the van, ending the battle.

According to Reuters, the state broadcaster, Rupavahini TV, reported that special forces troops also killed the rebels' intelligence chief, Pottu Amman, and Soosai, the head of the group's "Sea Tiger" naval wing.

European Union nations this morning called for an independent war crimes investigation into the killing of civilians in Sri Lanka. The British foreign secretary, David Miliband, said there had been "very grave allegations" of war crimes on both sides of the conflict and "they should be properly investigated".

In London overnight there were violent clashes outside the Houses of Parliament involving pro-Tamil demonstrators. A Scotland Yard spokesman said 10 protesters were arrested for a variety for public order offences and a total of 21 officers were treated for minor injuries today as they dealt with the protest. Eight people were reportedly taken to hospital.

In a statement, EU foreign ministers appealed to the Sri Lankan government to let UN aid groups into the country to help provide food and medical care to civilians caught in the fighting and to seek reconciliation with the country's minority Tamil population. Yesterday, Gordon Weiss, a UN spokesman, expressed concern about the fate of up to 80,000 people in the combat zone.

A military spokesman said 250 rebels had been killed in the final battle, after 72,000 civilians fled the small war zone over the weekend. According to UN figures, an estimated 7,000 ethnic Tamil civilians were killed between 20 January, when a military offensive pushed the rebels into a tiny enclave in the north-east, and 7 May.

The army commander, Lieutenant General Sarath Fonseka, told state TV: "We can announce very responsibly that we have liberated the whole country from terrorism."

The Press Trust of India said the army was withholding an official announcement of Prabhakaran's death until the completion of DNA tests.

Earlier, the military confirmed the deaths of four other leaders of the LTTE, including Prabhakaran's eldest son, Charles Anthony. State television broadcast images said to be of Anthony's body.

Prabhakaran was shot dead after government troops moved into the last areas of territory held by the group, according to the Sri Lankan army.

An unnamed military source told Reuters: "It was confirmed Prabhakaran was killed when trying to flee in an ambulance before dawn. We are waiting for the official announcement by the president."

Earlier today, troops found the body of Anthony, who was reportedly also a leader of the rebel group. The defence ministry said special forces found the bodies of the rebels' political wing leader, Balasingham Nadesan, the head of the rebels' peace secretariat, Seevaratnam Puleedevan, and one of the top military leaders, known as Ramesh.

In a statement it said the bodies of many more rebels were scattered about the area and were not yet identified.

Reports of Prabhakaran's death prompted celebrations in the capital, Colombo, but also protest at Britain's perceived support for the Tamils.

More than 1,000 demonstrators gathered outside the British high commission, where protesters burned an effigy of Miliband.

They threw rotten eggs and stones at the embassy compound, and the effigy was set on fire before being thrown over the high walls.

The foreign secretary has repeatedly called for a ceasefire in the conflict and for civilians to be allowed to leave the afflicted area.

The developments come after Sri Lanka's president, Mahinda Rajapaksa, announced on Saturday the defeat of the Tamil rebels, and soldiers seized control of the entire coast for the first time in the war.

Rebel official Selvarasa Pathmanathan said in a statement emailed to Associated Press: "This battle has reached its bitter end.

"It is our people who are dying now from bombs, shells, illness and hunger. We cannot permit any more harm to befall them. We remain with one last choice to remove the last weak excuse of the enemy for killing our people. We have decided to silence our guns."

Meanwhile, a group calling itself the High Security Zone Residents' Liberation Force today threatened to take the war onto the streets of Sri Lanka's towns and cities. A group using the same name has claimed responsibility for previous suicide bombings. It has been regarded as a front for the Tamil Tigers.

The Sri Lankan military has warned that sleeper cells around the country are expected to continue to operate even after the defeat of the LTTE's main military force.

Brigadier Udaya Nanayakkara, the military spokesman, told the Guardian last month that he expected the LTTE to resort to guerilla tactics once the military campaign was concluded. "It is not going to end soon," he said. "It will take some time to completely eradicate terrorism from the country, we think about two years."