By Chloe Arnold BBC correspondent in Colombo

The Tigers say a proxy war is being waged against them

Gunmen opened fire on the two men as they drove past on a motorbike on Friday. A third person was injured.

The rebels are blaming the attack on a rival faction led by Colonel Karuna, who split from the Tamil Tigers in the north in March.

The killings are the latest in a recent surge of violence between the two groups - and cast a shadow over the peace process in Sri Lanka.

The Tigers accuse the Sri Lankan military of supporting the breakaway leader and waging a covert war against them.

Norwegian peace brokers say the escalation of violence between Colonel Karuna's forces and the rebels in the north is the most serious threat to the peace talks since a ceasefire came into effect in February 2002.