MADRID (AFP) - Spanish intelligence agents were working urgently Wednesday to track down three journalists from Spain, the latest foreigners to go missing while reporting in war-torn Syria.

Prime Minister Mariano Rajoy said "no theory is being ruled out" in relation to the disappearance of the three, missing for 10 days in a war zone where numerous foreigners have been kidnapped in the past.

Spain's foreign minister said embassies and the intelligence service were "fully active" in the search.

The journalists have not been heard from for 10 days.

They had been reporting in Aleppo, a city in northwestern Syria that has been devastated by fighting, the Spanish press federation FAPE said.

Officials could not yet confirm whether the men had been kidnapped.

The case raised memories of three other Spanish reporters who were seized by the militant group Islamic State in northern Syria in 2013 and released in March 2014.

Foreign Minister Jose Manuel Garcia-Margallo called for caution over reports that the Spaniards were seen being taken away by men in an area of Aleppo controlled by several rebel groups.

"No demands have been made so far" by any would-be captors, said Garcia-Margallo.

"Leave us to work discreetly, because believe me, that is the best thing for your colleagues," he said, adding "there are people from (Spain's) National Intelligence Centre in Syria helping us".

A local monitoring group, the Syrian Observatory for Human Rights, cited witnesses saying the three were seen being taken away in the Maadi district on July 13.

Garcia-Margallo said he had been in contact with various embassies, United Nations representatives as well as Spanish intelligence operatives in Syria.

"No theory is being ruled out. The only thing we know for sure is that they have disappeared," Rajoy said in comments quoted by Spanish news agencies and confirmed by an official source.

WAR-ZONE SPECIALISTS

The Spanish press federation FAPE identified the three journalists as Jose Manuel Lopez, Antonio Pampliega and Angel Sastre.

They entered Syria via southern Turkey on July 10 and were last seen on July 12, said Elsa Gonzalez, president of the FAPE.

They had been working recently for various Spanish media.

"In that region there is intense fighting going on, so there is cause for concern," she said.

The journalists' families called for "respect" and "the greatest possible discretion" in the case, in a statement quoted by Spanish media.

Pampliega, a freelance war reporter born in 1982, contributed to AFP's text coverage of the civil war in Syria for a period up to 2013. A passionate reporter who tends to focus on human interest stories, he has also contributed to AFP's coverage in Iraq.

Lopez, born in 1971, is a prize-winning photographer who contributed images to AFP from several war zones, including from the Syrian conflict up until 2013 and Iraq in 2014. He has frequently teamed up with Pampliega.

Sastre, 35, has also worked in trouble spots around the world for Spanish television, radio and press. "Courage!" was his last word on his Twitter accound, July 10th.

SYRIA DANGEROUS FOR MEDIA

Media rights group Reporters Without Borders ranks Syria as the most dangerous country in the world for journalists.

It says at least 44 journalists have been killed since the conflict broke out in 2011 in Syria, where various armed factions are battling President Bashar Al-Assad's regime and each other.

In August 2014, Islamic State in Iraq and Syria (ISIS) decapitated US journalist James Foley, who was seized in northern Syria in 2012.

According to RSF, there are nearly 30 journalists, including nine foreigners, currently missing or held hostage in Syria.

"We are concerned about the safety of our Spanish colleagues", said International Federation of Journalists deputy general secretary Anthony Bellanger.

"We call on all factions involved in the country's conflict to respect press freedom".

In 2013, three other Spanish journalists were seized by Islamic State: El Mundo correspondent Javier Espinosa, freelance photographer Ricardo Garcia Vilanova and Marc Marginedas of El Periodico newspaper. They were all released.

Friends of a Japanese journalist, Junpei Yasuda, have been quoted by media as saying they have not heard from him since late June, and believe him to be in Syria.

The Japanese government said it had no information to indicate Yasuda had been detained or was in Syria.