Sri Lanka's Tamil Tiger rebels say peace talks with the government are "impossible" while heavy fighting continues between the two sides.
There have been months of violence despite an official ceasefire
The government had said it received a message from the Tigers on Friday via ceasefire monitors, saying they were ready to talk.
But a senior rebel spokesman, Seevarathnam Puleedevan, denied this.
About 60,000 people are now living in shelters after fleeing the fighting in the north and east of the country.
Sri Lanka's northern Jaffna peninsula has seen more heavy shelling and artillery fire as government forces and the Tigers battle for control of key areas.
The Sri Lankan military said the rebels had attacked an island off the peninsula, but that the area remained under government control.
In separate fighting near the eastern town of Batticaloa, police say commandos targeted a rebel camp.
Shelling has also been heard around the north-eastern town of Trincomalee.
There has also been violence away from the front lines.
On Saturday, a senior government peace official, Ketheesh Loganathan, was shot dead in the capital, Colombo.
He was the deputy head of the government's peace secretariat, which co-ordinates the Norwegian-brokered peace process between the government and rebels.
A spokesman for the Norwegian ceasefire monitors, Thorfinnur Omarsson, said the Tigers had contacted them to request renewed talks.
Palitha Kohona, the chief of the peace secretariat, told the Associated Press news agency that the government "gave a very positive answer and we said we will start talks immediately".
But Mr Puleedevan told AP: "The Sri Lankan government's offensive attacks make peace talks and the implementation of the cease-fire agreement impossible.
"The government must take the responsibility for the negative atmosphere."
The recent flare-up in fighting has alarmed Sri Lanka's key foreign donors - the US, Japan, the European Union and Norway - who have called for an immediate end to the hostilities, which they said was "seriously unravelling" the 2002 ceasefire agreement.
They also expressed serious concern about the humanitarian situation.
The ceasefire aimed to halt more than two decades of war between the government and the rebels, who are fighting for an independent homeland for the country's minority Tamil people in the north and east.
It remains officially in effect, despite months of violence.