"All those organisations ... have made a lot of allegations saying that the army bombed hospitals. But when we moved in, we proved that no [bombing] had taken place," he said.
'Breaking international law'
HRW said in a statement on Friday it had documented at least 30 artillery and air attacks on permanent and makeshift hospitals in the combat area since December 2008.
One of the deadliest raids took place on May 2, HRW said, when artillery shells struck Mullaivaikal hospital in the government-declared "no-fire zone," killing 68 people and wounding 87.
The group said that government military commanders responsible for ordering the alleged aerial and artillery attacks should be prosecuted for war crimes.
"Hospitals are supposed to be sanctuaries from shelling, not targets," said Brad Adams, the Asia director of HRW.
"While doctors and nurses struggle to save lives in overcrowded and under-equipped facilities, Sri Lankan army attacks have hit one hospital after another."
The group has criticised both the Sri Lankan armed forces and the separatist Liberation Tigers of Tamil Eelam (LTTE) for breaking international law during fighting in recent months and for putting civilian lives at risk.
Safe zone 'attacked'
The Sri Lankan government has denied using heavy weapons in the war zone and says it is taking care not to harm civilians.
But Meenakshi Ganguly, a senior researcher with HRW in Mumbai, told Al Jazeera: "There is a 'safe zone' that has been declared by the government, there are hospitals in that 'safe zone' - and those are the hospitals that have been struck.
"Both sides are responsible for violating international humanitarian law and the laws of war because a hospital, if considered a place where it is a safe sanctuary, should not be used in any kind of combat.
"They are repeatedly shelling hospitals in a safe zone," she said.
The ongoing fighting between the military and the LTTE has sparked international concerns over the plight of civilians trapped in rebel-held territory.
Thousands of people have fled the area but the UN has said that up to 50,000 civilians could still be trapped.
Sri Lanka says troops are on the verge of defeating the LTTE, which has been battling government forces for more than two decades to carve out a separate homeland for the country's minority ethnic Tamils.
The LTTE has reportedly suffered huge losses in recent fighting and is now confined only to a small patch of land in the island-country's north.