Undated handout photo by pro-rebel Tamilnet.com website shows what it claims are wounded Tamil civilians at makeshift hospital inside rebel-held territory (12 May 2009)

A doctor in Sri Lanka's northern war zone says at least 35 civilians died Wednesday when a mortar hit the only remaining medical facility there.

The attack follows a similar strike Tuesday, when at least 47 patients were reported killed.

The International Committee of the Red Cross also said one of its workers along with his mother were killed in shelling Wednesday. The organization did not say who was responsible for the attack.

ICRC officials said current fighting between the military and Tamil Tiger rebels is so heavy that for a second day in a row, the group's ferry cannot deliver medical supplies or transport wounded from the combat zone.

Meanwhile, Human Rights Watch says satellite images, along with witness accounts, contradict government claims that its armed forces are no longer using heavy weapons in the densely populated region.

The New York-based group said in a statement late Tuesday, a health official in the area had told them the weapons were being fired from an area under government control.

HRW also said witnesses have described sheltering from artillery attacks and being prevented by the Tamil Tiger rebels from escaping to government-controlled areas.

The group's Asia director, Brad Adams, said neither the army nor the rebels appear to have any reluctance in using civilians as "cannon fodder."

The United Nations aid agencies said they have little access to an estimated 50,000 civilians who are trapped in the conflict zone. 

Some information for this report was provided by AFP and AP.