Children stand in front of tents at the Manik Farm displaced persons camp in Vavuniya in Sri Lanka. UN Secretary General Ban Ki-moon visited the displacement camp on Saturday. (Kirsty Wigglesworth/Associated Press)Sri Lanka's president on Sunday rejected a call by the United Nations secretary general to lift restrictions on aid delivery to overcrowded displacement camps, saying the army must first finish screening the hundreds of thousands of Tamil refugees.

President Mahinda Rajapaksa's statement came in response to an appeal by Ban Ki-moon, made during his 24-hour visit to Sri Lanka, for unfettered access for aid agencies to the camps, where nearly 300,000 Tamils were herded during the final stages of the war against Tamil Tiger rebels.

The government proclaimed victory last week in the 25-year insurgency by the rebels, formally called the Liberation Tigers of Tamil Eelam, who sought to create an independent Tamil nation in Sri Lanka's north and east.

Ban's hurried visit was intended to press the government to ease what aid agencies described as a humanitarian crisis in the camps, with inadequate food supplies and reports of epidemics because of improper sanitation.

But Rajapaksa said security had to be assured "in view of the likely presence of LTTE infiltrators" among the refugees.

"As conditions improved, especially with regard to security, there would be no objections to such assistance, from organizations that were genuinely interested in the well-being" of the displaced Tamils, he said.

Fear that aid groups sympathize with separatists

The wording appeared to reflect widespread mistrust among many Sri Lankans who believe some humanitarian agencies have a pro-Tamil political agenda.

The bluntness of the president's statement contrasted with the milder tone of a joint communique with Ban, released almost simultaneously.

In that statement, Ban said the UN would continue providing humanitarian assistance to the displaced people, and Rajapaksa promised to "continue to provide access to humanitarian agencies."

After visiting the barbed wire-enclosed Manik Farm camp Saturday, Ban described conditions as "very, very difficult. It's a real challenge." He said the government lacked the resources to deal with the problem, but that the UN could fill the gaps.

"It was a very sobering visit, very sad, very moving," he said.

Shelling came from both sides in the conflict, refugees say

Civilians told Ban they had escaped the war zone after coming under intense shelling from both the rebels and the government.

"We ran for our lives from the shelling in the north," said one man who gave his name as Krishnathurai. "It was coming from both sides, the Tamil Tigers and the military, and we were stuck in the middle."

Ban then flew over the former battleground to see for himself, and saw a wasteland of scorched earth, shell craters and burned-out vehicles and tent camps.

The government has denied firing heavy weapons into an area that had been densely populated with civilians who had been kept there against their will by the rebels. But the helicopter tour given by the military to Ban and a group of journalists revealed widespread devastation.

In the joint statement, the government pledged to rebuild democracy in territory recaptured from the rebels and to reintegrate child soldiers conscripted into the rebel army.

Ban and Rajapaksa acknowledged the government "faces many immediate and long-term challenges" in providing relief, resettlement and reconciliation with the northern Tamils.

Rajapaksa said the government was committed to rebuilding democratic institutions and electoral politics in the north.

Until the latest army offensive, the Tamil Tigers had run a de facto government in roughly one-third of the island, with their own police force, courts, tax system and bureaucracy.

The rebels typically recruited at least one child from each family for their military force. Rajapaksa pledged to work with UNICEF, the UN children's agency, to reintegrate those child soldiers into society.

Sri Lankan PM promises to promote unity, equal rights

In the last week Rajapaksa has made repeated gestures to the Tamils, who comprise 18 per cent of the country's 20 million people, promising equal rights and unity. Tamils complain of systematic discrimination and harassment.

On Sunday, the president reiterated his plan to resurrect a long-dormant 13th constitutional amendment which would strengthen provincial administrations and allow a greater degree of autonomy to ethnic Tamil majority regions. The amendment was part of an Indian-brokered peace deal in 1987, but the rebels rejected the offer, saying the powers it gave were inadequate.

Ban welcomed the government's plan to dismantle the displacement camps and to return the bulk of the Tamils to their original homes before the end of the year, and called on donor countries to provide financing.

Rajapaksa said the return of the refugees was contingent on clearing landmines from the areas, and asked for international assistance.