(Reuters) - Police in Spain's North African enclave of Ceuta arrested four men on Saturday suspected of belonging to a militant Islamist network that may have been planning an attack in Spain, the interior ministry said.

Spain has stepped up security as well as efforts to prevent the radicalization of young Muslim citizens following attacks in Paris this month in which Islamist gunmen killed 17 people.

Confirming the arrests, Spanish Interior Minister Jorge Fernandez Diaz told reporters: "They are two pairs of brothers, highly radicalized and highly trained."

Diaz said there were "many parallels" with the two brothers who attacked the Paris office of the satirical newspaper Charlie Hebdo earlier this month, shooting dead 12 people. He did not elaborate.

El Mundo newspaper quoted Diaz as saying the four detained brothers were of Moroccan origin but held Spanish nationality. In searches carried out alongside the arrests, police found combat gear and knives, he added.

Earlier, the interior ministry released a short statement saying police were investigating whether the four men had been planning an attack in Spain. Authorities in Ceuta, an autonomous Spanish city bordering Morocco, declined to comment.

Sources close to the investigation told El Pais newspaper the probe had started two weeks ago when one of the four posted a video on his Facebook page showing him providing military training and urging others to wage jihad.

Spain is among a number of European countries struggling to deter young Muslim citizens from becoming jihadists in Syria or Iraq, fearing they might return to plot attacks on home soil.

The Spanish cabinet has said it will put forward a plan to counter radicalization among Muslim citizens at its weekly meeting next Friday.

Spanish and Moroccan police arrested seven people in December in a joint operation to prevent the recruitment of women to go to Syria and Iraq to support Islamic State insurgents there.

Last September, Spanish police arrested nine people suspected of belonging to a militant cell linked to Islamic State in Melilla, another Spanish enclave on the northern coast of Africa.

(Reporting By Sonya Dowsett; Editing by Gareth Jones)