Sri Lankan war planes struck a Tamil Tiger base Friday, the third straight day of bombing, government spokesman Keheliya Rambukwella said.

"The airforce carried out another round of aerial attacks against the Tigers today in the Trincomalee area," said Rambukwella, the policy planning minister and government spokesman on defence.

He said the bombing campaign was aimed at opening an irrigation canal shut down by the Tigers that had deprived water to a large farming community in the area.

Members of the Swedish-led Sri Lanka Monitoring Mission (SLMM) had gone to the area in a bid to settle the water issue, Rambukwella said.

Finland became the first country to announce a withdrawal after the rebels demanded European Union (EU) member states stop monitoring a Norwegian-arranged ceasefire in place since 2002.

Officials said artillery exchanges followed air strikes that started Wednesday against positions of the Liberation Tigers of Tamil Eelam (LTTE) in northeastern Trincomalee.

The LTTE admitted losing six of its cadres on Thursday when five more were wounded.

Two policemen were shot dead in Trincomalee Friday by suspected Tiger gunmen, police said, pushing the death toll since violence flared in December to at least 910.

Finland is one of three EU member states providing staff for the SLMM.

"Based on the fact the LTTE are not going to guarantee the monitors' safety after September 1, we will recall our observers by then," foreign ministry official Marita Maunola told AFP in Helsinki.

The Tamil Tigers demanded that observers from Denmark, Finland and Sweden leave the island after the EU added the LTTE to its list of "terrorist" organisations in May. That would leave only Norwegian and Icelandic monitors.