Jets are said to have carried out raids deep inside rebel-held territory
Sri Lanka's military says its jets have bombed a Tamil Tiger intelligence centre in the north, a day after a rebel air raid on a military base.
Fighter aircraft pounded the rebel centre in the northern region of Kilinochchi, the defence ministry said.
Reports from the area confirm an air raid, injuring at least two people. The rebels said civilian homes were hit.
The attack came as UN Secretary-General Ban Ki-moon expressed deep concern over the increased hostilities in Sri Lanka.
On Monday, the government issued a notice to foreign aid workers to leave the rebel-held areas in the north saying it could not guarantee their safety. On Tuesday, UN officials said they would relocate staff.
The government says that it is on track to defeat the rebels.
Officials said the area where the latest military operation was carried out is deep inside rebel-held territory.
"Taking on offensive raids into the LTTE [Liberation Tigers of Tamil Eelam] backyard, Sri Lanka air force fighter jets made precision air sorties at the LTTE's main intelligence command and control centre located in Kilinochchi," the defence ministry said.
The region also houses several non-governmental organisations (NGOs) and aid agencies. The UN said one of its vehicles was slightly damaged.
The Tamil Tigers said the air force had bombed a civilian settlement near Kilinochchi town centre, destroying 12 homes.
"No one was hurt because people sought safety in the bunkers," a statement said.
Photographs on their website showed buildings they said were civilian houses damaged or destroyed by the bombing.
Hospital officials told the BBC a pregnant woman had been injured in the bombing. She lost her baby after a stone hit her abdomen during the raid. A child also fainted.
Rubble of civilian homes the Tigers say were hit in the raid
There is growing concern for the fate of civilians in the north after the government ordered aid agencies to leave Tamil Tiger controlled territory.
The UN secretary general said the fighting had "grave humanitarian consequences for civilians".
"He reminds all concerned of their responsibility to take active steps to ensure the safety and freedom of movement of civilians, allowing humanitarian organisations to do their work in safety, as well as to reach persons affected by the fighting who need humanitarian assistance," a statement said.
Human rights group Amnesty International called for international monitors to be allowed into the north to oversee convoys of aid and other essential supplies.
There are about 70 UN national and international workers in areas of the north controlled by the Tamil Tigers, the UN says. Most are based in the town of Kilinochchi.
Aid agencies say there are nearly 160,000 people in the Tiger-controlled north who have been displaced by the fighting.
The International Red Cross (ICRC) - one of the most prominent international agencies in the north - said that its teams were committed to remain in both rebel and government-held areas.
But an ICRC spokesman said that situation was being monitored and negotiations were currently underway with the government in Colombo.
The UN says the plight of civilians in the north is worsening
Correspondents say that part of the problem for some aid agencies in the north is that their staff cannot leave because they are Tamil locals and the rebels will not issue them with passes.
The military meanwhile says that its offensive - aimed at crushing the rebels and ending their fight for a separate state for the Tamil minority - is on course.
The ministry of defence said that it shot down a rebel plane on Tuesday in a major incident in which 12 soldiers and a policemen were killed during a Tamil Tiger attack on a base in the northern area of Vavuniya.
The Tigers said 10 of their suicide fighters were killed in the raid.
They said that the raid was backed by artillery and light aircraft dropping bombs and that a radar station was destroyed in extensive damage to the base.
The Tamil Tigers have been fighting for a separate state for the Tamil minority in the north and east of Sri Lanka for 25 years.
More than 70,000 people have died.