By Frances Harrison
BBC correspondent in Colombo
A senior Tamil Tiger leader in Sri Lanka says 1,800 fighters have deserted from Colonel Karuna, the breakaway commander in the east.
Colonel Karuna's side deny mass desertion reports
But a spokesman for the colonel rejected the claim and instead blamed the main faction of the Tigers for the killing of an election candidate.
Rajan Sathiyamoorthy was killed in the eastern town of Batticaloa on Tuesday.
Both sides have been building up troops on the river dividing their territories in eastern Sri Lanka.
The mainstream Tigers say the fighters left Colonel Karuna either by going to stay with families and friends or by switching sides.
But a spokesman for Colonel Karuna, Varathan, laughed off the allegations made by the head of the Tiger's Peace Secretariat, Puleethevan.
The secretariat plays a key role within the Tamil Tigers in negotiations with the government - the talks broke down last year.
The head of the secretariat, Puleethevan, said he did not know how many fighters Colonel Karuna still commanded,
But he said those that were under his command were virtual detainees.
Meanwhile both sides have been strengthening their positions on the river which divides their territories in eastern Sri Lanka.
They say the situation is calm, but according to Colonel Karuna's spokesman they have deployed 700 fighters on the southern side of the river to match the same number deployed on the opposite bank.
He said instead of fighting directly the northern leadership was targeting civilians instead.
Varathan said that the murdered candidate in Friday's elections was a staunch supporter of Colonel Karuna and that was why he had been killed.
He said all but one of the remaining 18 Tamil National Alliance candidates in Batticaloa and Ampara were still loyal to the breakaway faction of the rebels.