Tamil rebels fired at a navy camp in northwestern Sri Lanka early on Thursday, injuring at least one sailor, a military spokesman said.
Brig Prasad Samarasinghe said the separatist rebels arrived on two boats and fired at the navy camp in northwestern Mannar, wounding the sailor.
Naval forces fired back, forcing the insurgents to retreat, he said.
Fighting between the Tigers and security forces has escalated in recent months.
The rebels have been fighting since 1983 to establish an independent homeland for Sri Lanka's minority ethnic Tamils following decades of discrimination by the Sinhalese-dominated government.
A 2002 truce is still officially in effect, but has virtually collapsed since the resurgence of large-scale fighting last year.