During the five-day trip, Mr Ashdown will tour refugee camps in Macedonia and Albania and visit the problem areas near the borders with Kosovo. The British Embassy is also setting up meetings with senior politicians in both countries and commanders of the Kosovo Liberation Army.
Downing Street confirmed yesterday that the Liberal Democrat leader was taking three letters from Mr Blair - to the Albanian prime minister Pandeli Majko, the Macedonian president Kiro Gligorov and the Macedonian prime minister Ljubco Georgievski. Mr Blair is concerned that the Macedonians in particular, who have been swamped with around 129,000 refugees, could withdraw their support for the humanitarian effort. Yesterday, Macedonia said it would not allow any more refugee camps to be built on its territory.
Mr Ashdown, who has made several trips to the Balkans in the past, will give Mr Blair a full report on his return.
The Prime Minister is planning to visit a Royal Air Force base in Germany on Tuesday. He also intends to fly to Brussels for a meeting with Javier Solana, secretary-general of Nato, to discuss the alliance's handling of the Kosovo crisis.
Mr Ashdown believes that the conflict is now "coming to a head" and that the Nato operation will enter a "new phase" over the next week. "Nato is going to step up its campaign and see if they can reach some kind of conclusion in the next week to 10 days," he said. "We are going to see air attacks intensifying, pilots taking more risks and we have to be prepared for the fact that there are likely to be some casualties on our side and more civilian casualties."