Over 21 Tamil Tiger rebels have been gunned down by security forces in Sri Lanka's [Images] embattled north in the last 24 hours.

The rebels attempted to breach the Muhamalai forward defence line in northern Sri Lanka late on Wednesday night, leading to clashes between the Tigers and the security forces, defence spokesman Udaya Nankara said.

While 14 rebels were gunned down by the security forces on Wednesday night, as many as seven were killed on Thursday, he said, adding that four Tigers were also arrested during the incident.

LTTE transmissions confirmed that one of their area leaders was among the dead. However, there was no immediate reaction from the rebels.

In a separate incident, two civilians were killed and 17 others, including two policemen, injured when a bomb planted in a bicycle exploded, the Army said.