The city is held variously by loyalist forces, extremist groups including the al Qaeda-affiliated al-Nusra Front, and other anti-government militia. ISIS also lurks on the fringes of the devastated city.
The three men -- Antonio Pampliega, Jose Manuel Lopez and Angel Sastre -- appear to have entered Syria from southern Turkey on July 10. They have not been heard of since July 13. A local fixer who was reportedly working with the men has also gone missing.
"We are now working to find them but for the time being we don't know where they are," a joint statement from the mens' families read, which also asked for "as much discretion as possible" in order to help locate them.
A source at the Ministry of Foreign Affairs in Spain confirmed to CNN that the three men had gone missing.
"We are aware of the situation and are working to solve it as soon as possible," the source said.
Spanish daily El Pais reported
that government sources refused to assume that the reporters had been kidnapped but conceded that there were indications that they had been abducted.
The Madrid Press Association released a statement saying that it was confident that the Spanish government would be able to locate the men.
Spanish Justice Minister, Rafael Catala, said that the disappearances were "very bad news" but that the Spanish government would wait for confirmation of the exact circumstances, the Spanish wing of the international journalist organization Reporters Without Borders, which is also known by its French acronym RSF, reported
RSF also expressed concern over the fate of the three Spaniards.
Appeals to the Spanish government
"We are very concerned about the fate of these three Spanish journalists, who disappeared in Aleppo, a city controlled partly by Islamic State and partly by Al-Nusra Front, another armed group," Reporters Without Borders secretary-general Christophe Deloire said.
"We urge the Spanish government to use all possible means to find these journalists and we appeal to all parties to the conflict to respect the work of the media and to stop taking hostages for political ends. The UN Security Council's recent Resolution 2222 pointed out that journalists covering armed conflicts are civilians, that they cannot be deliberately targeted and that they enjoy special protection."
The three men, all members of the RSF organization, are freelance journalists and experienced war reporters, and have covered conflicts from the field before. Sastre worked for CNN's now-defunct Spanish affiliate CNN+ and has appeared
on CNN's Spanish-language sister network, CNN En Español, discussing the spread of ISIS.
Syria remains one of the most hazardous countries for journalists to report from. News of the missing Spanish journalists comes less than a month after Japanese journalist Jumpei Yasuda went missing
after crossing the Turkish-Syrian border. He has not been heard of since June 23.