Russia and Georgia edged dangerously close to direct conflict today after Tbilisi launched an overnight offensive to regain control over the breakaway province of South Ossetia.

Fighting raged around the city of Tskhinvali, the South Ossetian capital, as Georgian troops backed by tanks and warplanes pounded separatist forces. At least 15 people were reported to have been killed.

The fighting had raised fears of an all-out war that could draw in Russia, which has peacekeepers in South Ossetia and which backs the separatists.

"There has been bombing on Georgian territory by the Russian Federation," said Mikhail Saakashvili, the Georgian President. "It is nothing but classic international aggression."

Unconfirmed reports said that three Russian peacekeepers were injured when their base was hit by missiles. Vladimir Putin, the Russian Prime Minister, accused Georgia of starting the hostilities. "It is sad, but this will provoke retaliatory measures," he said from Beijing, where he is attending today's Olympics opening ceremony.

South Ossetian officials said that much of Tskhinvali had been destroyed in the Georgian offensive. A Reuters correspondent some two miles from the city said that the roar of warplanes and the explosions of heavy shells was deafening and many houses were ablaze.

Mr Saakashvili said that most of South Ossetia was already under the control of Georgian forces but that fighting was continuing in the centre of Tskhinvali. The city was hit by air strikes and shelling throughout the night and missiles continued to batter it this morning.

This afternoon, however, the mayor of Tbilisi announced that Georgian authorities had declared a three-hour ceasefire from 1100 to 1400GMT to allow civilians to leave the conflict area. "We are offering amnesty for the separatist militants," Gigi Ugulava told Rustavi-2 television.

The area is of strategic importance, largely because of the BTC oil pipeline, which runs through central Georgia just south of the breakaway region. The pipeline - which features in the 1999 James Bond film The World is Not Enough - pumps around one per cent of global crude supplies from the Caspian to the Turkish port of Ceyhan for export to Western Europe but is already closed because of an attack in Turkey last week by the Kurdish separatist organisation PKK.

Georgia's Deputy Interior Minister, Eka Sguladze, said that three Russian Su-24 jet bombers flew into Georgia this morning and bombed the town of Gori and the villages of Kareli and Variani, injuring seven people.

Both Nato and the White House appealed for an end to the fighting and the International Committee of the Red Cross called for the establishment of a "humanitarian corridor" through South Ossetia.

Tensions between Georgia and Russia have been rising over the last few months over the two breakaway republics of South Ossetia and Abkhazia.

Georgia accuses Russia of fermenting trouble in both regions and supporting the separatist governments as a way to put pressure on Georgia and foil its attempts to join Nato.

Russia has given out passports to a majority of South Ossetians and Abkhazians.

The UN Security Council met to discuss the situation this morning but failed to agree on a Russian statement calling on both sides to renounce force.

The Russian envoy to the UN, Vitaliy Churkin, described Georgia's actions as "treacherous".

"The situation in the conflict zone has reached a dramatic line," he told the council. "Civilians, old people and children are under massive artillery shelling from Grad rocket systems, guns and large-calibre mortars."

President Medvedev of Russia, facing his first major crisis as president, was set to meet with his security council today and was considering emergency measures.

But Lado Gurgendize, the Georgian Prime Minister, said that Tbilisi had been forced to act to "restore peace". He told a Cabinet meeting: "These actions will continue until peace and order will finally be in place in the region."

A senior Georgian security official, Kakha Lamaia, told Reuters that heavy military equipment and armoured vehicles were entering South Ossetia through the Roki tunnel from Russia. "Our intelligence didn’t detect any regular Russian units, but detected heavy equipment and armoured military vehicles coming through the tunnel," he said.

Times Recommends

• Would you live on the wrong side of the Berlin Wall?
• Wish you were here, says Iraq tourist board
• Russian policeman’s corruption plea to Putin