BEIRUT (Reuters) - A Lebanese soldier was killed by a roadside bomb in northern Lebanon on Thursday, the National News Agency (NNA) and a security source said.

Three others, including one officer, were wounded in the explosion which took place near the town of Arsal close to the Syrian border, NNA reported from a military statement.

The army shelled positions of militants on Arsal's outskirts after the blast, the security source said.

Islamist militants are active in the area near the Syrian-Lebanese border. Fighters from Islamic State and the al Qaeda-linked Nusra Front briefly overran Arsal in 2014 before withdrawing after clashes with the army.

Nusra Front freed 16 Lebanese soldiers and policemen in December 2015 in exchange for jailed Islamists. It had captured the soldiers during the Arsal incursion in 2014. Islamic State is believed to be still holding nine soldiers it captured.

(Reporting by John Davison and Lisa Barrington; Editing by Louise Ireland and Mark Potter)