The Sri Lankan Government claimed an important victory in the country's brutal 25-year civil war yesterday after its forces captured a key Tamil Tiger garrison just four miles from Kilinochchi, the rebels' main base in the north of the country.

News of one of the deepest pushes into Tiger-controlled territory in a decade may allow the Sri Lankan President Mahinda Rajapaksa to save face after failing to deliver on his pledge to crush the rebels militarily before the end of 2008. An estimated 250,000 civilians have been forced to flee their homes in the face of the army's advance.

The Government said that ground forces supported by helicopter gunships and jets fighters overran the garrison town of Paranthan, just 4.5km from Kilinochchi, early yesterday morning after hours of bitterly fierce fighting. The fall of Paranthan, the site of an important crossroads which had been under rebel control for ten years, cut supply routes to other Tiger strongholds, a spokesman for the defence ministry said.

"Unable to withstand the fury of the combined army and air force onslaught, [Tamil Tiger] terrorists withdrew from [Paranthan] in total disarray," he added. The ministry said that at least 50 Tiger fighters had died but did not say what casualties government troops had suffered.

Accurate numbers on the losses being suffered in Sri Lanka are all but unobtainable because of a ban on media entering the conflict zone.

Both sides are known to exaggerate enemy losses and to under-report their own.

For months the Government has claimed that Kilinochchi is poised to fall, an event that could allow it to claim victory in Asia's longest-running civil war, a conflict that has claimed more than 70,000 lives. This week it escalated its air campaign on the surrounding region.

However, analysts say that even if Kilinochchi is toppled, rebel troops are likely to fight on in the surrounding dense jungle.

Meanwhile, the Government's escalation of the conflict has drawn a wave of criticism over an alleged surge in extortion, abductions and extrajudicial killings in army-held areas, with pro-government militias usually being blamed.

There was no immediate comment from the Tigers on the battle for Paranthan. The group is suspected to have been behind a suicide bombing that killed eight people at a military base in Colombo last week.

The two sides have provided very different accounts of how the offensive on Kilinochchi is progressing. Last week, P. Nadesan, a leader of the Tigers' political wing, told a rally in Kilinochchi that the Sri Lankan Army was suffering severe losses and that the region had become "an ultimate death trap" for government forces, according to a Tamil newspaper. Vellupillai Prabhakaran has called President Rajapaksa's promise to take Kilinochchi through force – a feat never accomplished by government troops -- "a daydream".

The rebel base is effectively the administrative centre of a parallel state that the Tigers, who are classified as a terrorist organisation by the US and the EU, have fought to establish to protect Sri Lanka's Tamil minority from a Government dominated by the ethnic Sinhalese majority.

The army pushed the Tigers out of eastern Sri Lanka in July 2007 and began an attack on the north this year after the Government formally scrapped a 2002 Norwegian-brokered truce in January.

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