A Spanish judge on Tuesday remanded in custody a man suspected of belonging to an al-Qaida linked militant group taking part in the Syrian conflict.

The judge ordered Abdelwahid Sadik Mohamed, 28, to be held in custody while he is investigated for the suspected crime of membership of a terrorist organisation because of the risk that he would flee or try to destroy evidence, according to a written ruling from the National Court.

King Juan Carlos told Britain that it was not in Spain's interest to take back Gibraltar as it would trigger claims from Morocco for Spanish territories, newly declassified documents from the 1980s show.

The king admitted in a private conversation with the then British ambassador to Madrid, Richard Parsons, that "it was not to the advantage of Spain to recover Gibraltar in the near future".

Spanish King Juan Carlos's youngest daughter, Princess Cristina, has been hurled into the center of a corruption scandal that swept up her husband, Inaki Urdangarin, and outraged the nation.

The blonde-haired, 48-year-old Cristina, once known for her easy smile, was summoned Tuesday to appear on March 8 before a court in Palma on the Mediterranean island of Majorca as a suspect in alleged tax and money-laundering crimes.

Japan's foreign minister left for Spain and France on Tuesday, where he was expected to press Tokyo's case in its spat with China.

In a message on his ministry's Facebook page, Fumio Kishida noted the visits were his first of the new year.

A Spanish court summoned King Juan Carlos' youngest daughter Cristina as a suspect in alleged tax and money-laundering crimes Tuesday, a historic first for a direct relative of the monarch.

Cristina, 48, has been linked to the business affairs of her husband, former Olympic handball player Inaki Urdangarin, who is under investigation for alleged embezzlement of public funds.

Spanish police on Sunday arrested a suspected member of an al-Qaida-linked militant group fighting in Syria, authorities said.

The suspect Abdelwahid Sadik Mohamed, a Spaniard, "is accused of taking part in the 'holy war' in Syria", the interior ministry said in a statement.

Sixty-two percent of Spaniards want their country's scandal-hit King Juan Carlos to abdicate and fewer than half support the monarchy in general, a poll published on Sunday showed.

A majority however support the king's son and heir Felipe and believe he could restore the family's prestige, according to the study by pollster Sigma Dos for El Mundo newspaper.

A group of nuns in Spain got a New Year surprise when they checked their answerphone machine to discover they had missed a call from the Pope, who left a message asking why they didn't pick up.

"What can the nuns be doing that stops them answering the phone?" said Pope Francis, chuckling, in the message he left on New Year's Eve for the Barefoot Carmelites of Lucena, aired on Spanish radio on Friday.

Spain vowed Friday to stand firm on its policy on ETA prisoners even though jailed members of the armed Basque separatist group have softened their stance on key demands.

Last week EPPK, a collective representing hundreds of jailed members of ETA, western Europe's last major armed secessionist group, dropped its long-standing demand for a general amnesty.

Jailed members of the armed Basque separatist group ETA said Saturday they could use "legal channels" to seek their freedom, abandoning the group's insistence on an amnesty.

ETA, blamed for the deaths of 829 people in a four-decade campaign of shootings and bombings for an independent homeland in northern Spain and southern France, renounced its armed struggle in October 2011.