Hours before the Sri Lankan President is due to meet Tony Blair in London today, European ceasefire monitors have accused his security forces of the "assassination" of 17 aid workers from a French NGO.
Even as Mahinda Rajapakse meets Mr Blair to discuss the crisis in his country, the Sri Lankan military is accused of what has been called the most serious attack on humanitarian workers in the world since the bombing of the UN compound in Baghdad in 2003.
The accusation will increase the pressure on Mr Blair to push Mr Rajapakse for an end to the continuing violence between his forces and Tamil Tiger rebels in Sri Lanka, just days after his government launched a new offensive close to where the killings took place
Seventeen local employees of the French NGO, Action Contre la Faim, (ACF) were found dead in the town of Muttur earlier this month. Fifteen were found in the NGO's local office with bullet wounds to their heads. The bodies of two others were found in their car near by; they had apparently been trying to flee.
All 17 were wearing T-shirts which identified them as humanitarian workers. Each side has accused the other of the killings. Now, for the first time, unarmed European ceasefire monitors have accused government forces. The monitors said in a statement yesterday that they are "convinced that there cannot be any other armed groups than the security forces who could actually have been behind the act".
The statement called the killings a "gross violation of the ceasefire accord". The outgoing head of the monitoring mission, the retired Swedish general Ulf Henricsson, was blunter. He called the killings a "committed act of assassination" and "one of the most serious recent crimes against humanitarian aid workers worldwide".
The Sri Lankan government reacted furiously. "We deny it, and it's a totally baseless statement," said a spokesman, Keheliya Rambukwella. "It's pathetic and it's biased and they have no right make such a statement because they are not professionals in autopsy or post-mortem."
But the European monitors are one of the only parties in Sri Lanka respected for their neutrality. They have no axe to grind on behalf of the Tamil Tigers. Most of the monitors are being forced to withdraw after the Tigers threatened to target them in retaliation after the EU named the Tigers as a banned "terrorist" organisation.
The spokesman for the monitors, Torfinnur Omarsson, said they had interviewed hospital staff, police, relatives of the dead aid workers, and other eyewitnesses before coming to their conclusions. Several relatives have publicly accused the government.
The accusation is certain to hang over the meeting with Mr Blair today. Downing Street confirmed that Mr Blair is holding a "private meeting" with the Sri Lankan President, and that they would discuss the current situation in Sri Lanka.
Yesterday's allegations come after a disastrous few weeks for Mr Rajapakse's government. The UN children's organisation, Unicef, accused the Sri Lankan air force of killing children in an air raid, prompting the military to respond by saying: "If the children are terrorists, what can we do?"
International support for the government was strong until just over a month ago. But it has been seriously eroded since the government launched a ground offensive which has set off the worst fighting since the 2002 ceasefire.
Even so, the West is unlikely to drop all support for Mr Rajapakse in the face of the enemy he is fighting. The Tigerspioneered suicide bombing and have been blamed for trying to force the Sri Lankan government into war through a series of attacks. They are fighting for a homeland in the north and east of Sri Lanka.