COLOMBO, July 19 (Reuters) - Sri Lanka's top foreign donors urged the government and Tamil Tiger rebels on Tuesday to halt a spree of killings undermining a 3-=C2=BD year ceasefire, saying international support would be "deeply eroded" if the truce fails.
In a sternly worded statement, the European Union, the United States, Japan and Norway -- who have pledged the lion's share of $4.5 billion in aid to rebuild war-ravaged areas -- said it was time the foes proved they are committed to the ceasefire.
The statement comes after the Liberation Tigers of Tamil Eelam (LTTE) warned of an imminent return to the island's two-decade civil war and vowed to carry arms in military-held areas -- a move that could rupture the truce.
"If the Ceasefire Agreement ceases to function, the wider peace process would be gravely jeopardised and international support for that process would be deeply eroded," the donors warned, adding they were alarmed at the deteriorating security situation.
"The Co-chairs call on the government of Sri Lanka and the LTTE each to take immediate action to prevent killings," the statement added. "The Co-chairs believe that it is time the parties demonstrate the seriousness of their commitment to the Ceasefire Agreement."
The donors did not say whether the aid, which was pledged in 2003 and is separate from another $3 billion donors have promised to help rebuild areas hammered by December's tsunami, was in danger.
Dozens of rebel cadres, police, soldiers and civilians have been killed in recent months despite a 2002 ceasefire that has given Sri Lanka its longest spell of relative peace since the conflict began in earnest in 1983.
The army has stepped up patrols in the east as tension escalates over the violence, which it blames on feuding between the mainstream rebels and a renegade faction. The Tigers accuse the military of helping breakaway cadres mount attacks.
Analysts and diplomats fear the standoff could deteriorate into a direct armed confrontation which would in turn break the ceasefire and raise the spectre of a return to a civil war that has already killed more than 64,000 people.
However Nordic truce monitors say the violence has subsided since the rebels withdrew their political cadres from government-held areas in the east, and they are optimistic peace will hold.