Thousands of civilians are fleeing the fighting
A cross-party delegation of British MPs has held meetings with politicians and civil society figures on the first day of a two-day visit to Sri Lanka.
The visit is intended to focus on the emerging humanitarian crisis in the war-torn country.
Among the MPs are former defence minister Des Browne, whose appointment as special envoy to Sri Lanka was rejected in February by Colombo.
The MPs insist they are friends of Sri Lanka on a fact-finding visit.
The BBC's Charles Haviland in Colombo says that the government and its many supporters in the media are growing impatient, sometimes derisory, towards Britain and some other Western countries over their appeals for a stop to the fighting in the north-east.
The UK Foreign Secretary, David Miliband, said during a visit to the country last week that there was a "desperate need" for combat to stop in order to protect tens of thousands of civilians in the war zone.
The Tamil Tigers praised the UK and French foreign ministers for their visit, which they said highlighted the plight of civilians.
The TIgers have been fighting for the past 25 years for an independent homeland for Sri Lanka's minority Tamils in the north and east of the country.
In the last few weeks a sustained army offensive has forced the rebels into a tiny patch of land in the north-east.
The government says it is about to defeat them permanently and has accused Western leaders of hypocrisy in bombing suspected al-Qaeda hideouts yet trying to stop Sri Lanka from crushing the Tamil Tigers.
A statement on the defence ministry website at the weekend accused some diplomats of being responsible for "the plight of civilians under the clutches of terror".
Our correspondent in Colombo says that the atmosphere in relation to the visiting delegation of MPs may be strained at times.
Perhaps because of Sri Lanka's sensitive relations with the West, our correspondent says that the parliamentarians are keeping their visit low-profile and have not made any public statements.
However they are due to visit refugee camps in the north on Tuesday and are likely to renew appeals to both sides to initiate a ceasefire.
The Tigers have repeatedly said they want a ceasefire.
But the government says a ceasefire would get in the way of its objective of finally defeating the rebels.
Tens of thousands of civilians are still believed trapped in fighting between the army and Tamil Tiger rebels in the north-east.