MADRID (Reuters) - Two young Spanish women, one of them under 18, have been arrested in the Spanish North African enclave of Melilla on suspicion of trying to join an Islamic State militant cell in the Middle East, the Interior Ministry said on Monday.

The women were detained on Saturday trying to cross from Melilla into Morocco, where they planned to make contact with a network that would transport them to conflict zones in Iraq or Syria, the ministry said.

The older one was 19. The younger one was not identified but media reports said she could be as young as 14.

Thousands of young people have set off from European countries to join Islamist rebels fighting in Syria, often finding recruitment agents through social media.

Islamic State began as an al Qaeda offshoot in Iraq, seized territory in Syria after joining the rebellion against President Bashar al-Assad, and has now extended its area of control in a spectacular push across northern Iraq, declaring an Islamic caliphate in the area it controls.

"One of the main aims of (Islamic State leader Abu Bakr) al-Baghdadi is to recruit as many foreign combatants as possible ... The process of radicalization, recruitment and then transport to join up with combatants is perfectly planned and organized by a network operating in the Maghreb," the Spanish Interior Ministry said.

Last May, Spain said its police had arrested militants from an international Islamist cell suspected of recruiting fighters and sending them off to fight in Mali and Libya. In March, Morocco and Spain jointly said they had broken up a militant cell.

(Reporting by Raquel Castillo; Writing by Paul Day; Editing by Kevin Liffey)