JOIN USDefence spokesman and Minister Keheliya Rambukwella told reporters that troops have entered the safety zone amid resistance from the Liberation Tigers of Tamil Eelam (LTTE) Tuesday.
The safety zone, which is around 3 sq km, was readjusted by the government Friday and is part of a 6 sq km area along the coast in the north-eastern Mullaitivu district which the rebels are holding.
In the latest operations, some 90 more civilians were rescued by the military Tuesday.
Military spokesman Brigadier Udaya Nanayakkara said that troops advancing from two fronts toward the safety zone met with resistance but killed 25 rebels in one location and 10 more in another.
He said the rebels set off three suicide explosions as well.
The spokesman did not comment on military casualties.
The fresh moves came amid reports that over 400 civilians were killed over the weekend in the region.
The military and the LTTE have traded allegations as to who was responsible for the killing of the civilians.
UN Secretary General Ban Ki-Moon has called on the government and Tamil rebels to avoid further civilian casualties in the conflict in the island's north.
"The secretary-general is appalled at the killing of hundreds of civilians in Sri Lanka over the weekend," a statement from his office said.
"The secretary-general urges the government of Sri Lanka to explore all possible options to bring the conflict to an end without further bloodshed and to make public the terms under which that can be achieved without further loss of civilian life, and for the LTTE to give sober and positive consideration of those terms," the statement said.
Earlier the government said it would not use heavy weapons in the operation which they say is aimed at rescuing some 20,000 civilians trapped in the area.
UN agencies say the number civilians in a narrow land strip along the coastal area of Mullaitivu, 395 km north-east of the capital, is around 50,000.
The UN statement said the secretary-general has repeatedly called on both sides to stop using heavy calibre weapons in areas with high civilian concentrations.
The International Committee of the Red Cross has sent a ship with 30 tonnes of food for the civilians in the rebel-held area, but until noon the ship had not been able to get close to the coast for unloading due to the ongoing fighting, ICRC sources in Colombo said.
The ship is due to carry back some of the injured and ill persons as they have been doing in the past. Doctors in the conflict zone say they lack medicine to treat the injured.
The number of wounded was estimated at more than 1,200 since the incident Sunday.
Government troops say they are on the final phase of ending a major military operation aimed at crushing the rebels as well as rescuing civilians from the control of the Tamil Tigers.