Malaysia's military today said seven unidentified gunmen were seen near its base on the Thai border where a grenade attack left four soldiers injured.

Malaysia and Thailand have offered different explanations for the incident. Malaysia's defence ministry said two grenades were hurled into the Ban Di Samoe outpost in northern Kedah state before dawn Wednesday.

However, the Thai army said it was an accident that took place as some 50 Malaysian and Thai soldiers conducted a joint patrol.

Malaysia's deputy army chief Lieutenant General Muhammad Ismail Jamaluddin dismissed the Thai account, saying that no training exercises were being carried out at the time.

"There have not been any cross-border operations, they patrol the Thailand side and we patrol our side. No training (was) conducted by Thais in the area," he told reporters.

Muhammad Ismail said soldiers spotted the unidentified gunmen several hours after the attack as they cleared a landing strip near the base.

"There were seven unknown people dressed in black and dressed in balaclavas. We believe they were carrying M16s. We couldn't be sure because they were a long way away," he told reporters.

The soldiers were unable to detain them and they disappeared into the jungle, he said.

Isolated incident

Muhammad Ismail said the grenade attack was an isolated incident.

"We're not concerned at all. We are investigating who they are and what their motives might have been. At this point they remain unknown people with unknown motives," he said.

Malaysia tightened security on its border with Thailand last month, restricting entry and banning Thai motorcycles after a Malaysian border official was attacked by a group of Thai fuel smugglers.

Southern Thailand is in the grip of a three-year separatist insurgency, which has left 1,800 people dead.