Minister Peiris had earlier held talks with his Japanese counterpart Toshihiro Nikai and Foreign Minister Hirofumi Nakasone.
At a news conference, Minister Peiris reiterated that Colombo has no plan to probe allegations of war crimes and rejected international demands for a probe.
The minister said: "The world should not try to... emphasise everything that is negative, make things as difficult as possible for Sri Lanka, threaten economic sanctions."
Unnecessary pressure on the Sri Lankan government may even lead to a revival of terrorism in the country, he warned, without elaborating.
"What the country needs this time is support, understanding, empathy, not condemnation, not judgement... not posturing," he said.
Peiris said his government refrained from using heavy artillery and aerial bombardment attacks out of concern for civilians "at the expense of postponing the end of hostilities."
The United States and other governments had repeatedly called on the Sri Lankan government (GoSL) to cease pounding a narrow strip of land in which 300,000 people had concentrated on the government’s advice.
In mid-March, US Secretary of State Hillary Clinton telephone President Mahinda Rajapakse “to express the United States' deep concern over the deteriorating conditions and increasing loss of life occurring in the GoSL -designated 'safe zone'.”
“The Secretary stated that the Sri Lankan Army should not fire into the civilian areas of the conflict zone,” a State Department press release said.
More pointedly, as casualties mounted amid relentless shelling – even as US satellites observed – President Barack Obama demanded on May 13, “the [Sri Lanka] government should stop the indiscriminate shelling that has taken hundreds of innocent lives, including several hospitals, and the government should live up to its commitment to not use heavy weapons in the conflict zone.”
Last week, independent investigations by The Times and Le Monde newspapers found that up to 20,000 Tamil civilians had been slaughtered by government shells. The papers quoted UN officials as saying the UN knew, but sought to suppress reports to retain Colombo’s goodwill.
Regarding the controversy over an IMF loan Sri Lanka is seeking, Minister Peiris said that a decision on the disbursement of the funds "should not involve political considerations," but should be "dependent upon technical criteria."
Prof. Peiris was the chief negotiator for the then UNP government when it was in negotiations with the LTTE in 2002-3.
The UNP was defeated by the SLFP in 2004 and he switched sides two years later, along with fellow negotiator Milinda Moragoda.
Both men had been popular with Western backers of the peace process as was the UNP, given its enthusiasm for the neoliberal agenda for Sri Lanka.
During the Norwegian-brokered negotiations, Prof. Peiris was famously associated, along with LTTE chief negotiator, Anton Balasingham, with the ‘Oslo Declaration’, an agreement between both sides to explore federalism as a solution to the conflict.
At the time Peiris lauded the Oslo Declarations as a ‘paradigm shift by the LTTE’ and as a climb down by the Tigers from the demand of an independent Tamil Eelam state.
However, after crossing over to the Sinhala-nationalist government of President Rajapakse in 2006, Prof. Peiris rejected federalism as a solution.
"Today the intellectuals and experts worldwide agree that terms such as federalism, unitary and united have no clear definition and are indistinct at best," he was quoted as saying.
He added, without elaborating, that what was required was a "practical solution" to the ethnic conflict.