Confidential UN satellite images leaked yesterday appear to show that the Sri Lankan Air Force bombed a safe haven for up to 150,000 civilians fleeing fighting against the Tamil Tigers.

The images contained in an internal UN report may constitute the strongest evidence yet of violations of international humanitarian law or war crimes, according to human rights activists. The report by Unosat, dated April 26, provides detailed images of the tiny strip of beach and coconut grove — now covering only 3.8sq miles (10sq km) — where the army has pinned down the Tigers along with thousands of civilians.

The Government declared the area a safe haven or “no-fire zone” on February 12, urging civilians to seek shelter there, and has repeatedly denied using heavy artillery or aerial bombs to attack it.

The Unosat report, based on images between February 5 and April 19, appears to back up the persistent verbal testimony to the contrary from doctors, aid workers and civilians fleeing the area. “Within the northern and southern sections of the civilian safe zone, there are new indications of building destruction and damages resulting from shelling and possible airstrikes,” the report said.

Francesco Pisano, manager of the Unosat programme, told The Times that the report was compiled to assist UN agencies and aid organisations in Sri Lanka and was placed accidentally on one of their websites. He said that his analysts had concluded that some of the damage in the images could have been caused only by aerial bombing. “This kind of accuracy you acquire only with air power,” he said. “The craters beyond a certain size also make our analysts almost certain that these were air-dropped bombs.”

He declined to say which side was responsible. The army says that it destroyed the last of the Tigers’ small air wing when it shot down two of its planes over Colombo in February. Human rights activists said that the images required detailed analysis and further inquiries but could provide the hardest evidence yet that the army had shelled and bombed civilians.

“This is incontrovertible evidence that the Government has been lying for months,” Peter Bouckaert, emergencies director for Human Rights Watch, said. A Sri Lankan military spokesman was not immediately available for comment.

The images emerged as Sri Lanka rejected appeals for a ceasefire from David Miliband, the Foreign Secretary, and Bernard Kouchner, the French Foreign Minister. “We have at no time gone for a ceasefire. We will not do so now,” President Rajapaksa said. “I don’t need lectures from Western representatives.”

Sri Lanka published details of an apparently heated exchange over civilian casualties between Mr Miliband and Gotabaya Rajapaksa, the Defence Secretary, who is also the President’s brother. Mr Miliband told Parliament that any alleged war crimes should be investigated “urgently, independently and credibly”.

He hinted that Britain might join the United States in trying to use Sri Lanka’s application for a $1.9 billion (£1.2 billion) IMF loan as leverage in negotiations, as reported by The Times yesterday. “We are duty-bound to look extremely carefully at the situation on the ground should any plan be presented to the IMF board,” he said.

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