MADRID (AFP) - Seven people were arrested in Spain and Morocco on Tuesday in a probe on a network recruiting women to join the Islamic State in Iraq and Syria (ISIS) group.

Spain's interior ministry said four women, one of them a minor, and three men were arrested in Barcelona, Spain's North African enclaves of Ceuta and Melilla and in the nearby Moroccan town of Castillejos.

"All of the arrested are accused of forming part of a network that recruited and sent women to the Syria-Iraq front to the terrorist organisation Daesh," it said in a statement, using a term used by many governments use to call ISIS.

Police were searching six homes as part of the operation, which was carried out in cooperation with Moroccan security forces. About 100 Spaniard have joined "militias" in conflict zones in Syria and Iraq, Spain's ambassador to Iraq, Jose Maria Ferre de la Pena, told a conference in Madrid last month focusing on Islamic extremism.

That is fewer than the hundreds from Britain, France and Germany who are thought to have joined ISIS, which controls controls large swathes of Iraq and Syria and has killed several western hostages.

But the relatively sudden emergence of the phenomenon has shocked Spanish authorities, who have arrested dozens of suspects accused of planning to join ISIS.

Spanish police in August detained a 14-year-old girl and a 19-year-old woman in Melilla suspected of trying to join Islamic extremists fighting in Iraq and Syria. The two Spanish-governed enclaves of Ceuta and Melilla are Europe's only land borders with Africa.

The Spanish government has said it fears battle-hardened Islamist fighters may return to Spain from Syria and other conflict zones under the influence of groups inspired by Al-Qaeda, posing the threat of attacks.

Spain this year marked the 10th anniversary of the March 11, 2004, Al-Qaeda-inspired bombing of four packed commuter trains in Madrid, which killed 191 people.