Three Spanish freelance journalists who went missing in Syria last year and were believed to have been kidnapped, have been released, according to the Spanish Press Federation and the government.

Antonio Pampliega, Jose Manuel Lopez and Angel Sastre disappeared last July while working on an investigative report in the northern city of Aleppo, where other journalists have been captured in the past, Spanish media reported at the time.

The government said a plane brought them from Turkey to Spain on Sunday.

No details were immediately available on how the three were released, but their release had been "possible thanks to the collaboration of allies and friends especially in the final phase from Turkey and Qatar", the Spanish government said in a statement.

It was not clear whether ransom was paid to secure their release.

Al Jazeera's Stef Dekker, reporting from Gaziantep, said that the three men had gone through a thorough medical examination and seemed to be in good health.

"According to the three journalists, they were treated well by their captors," she said.

"We know from past negotiations, from past hostage releases, that money often changes hands."

Qatari mediation

Qatar's state news agency reported on Sunday that Sultan bin Saad al-Muraikhi, the Arab Gulf state's assistant foreign affairs minister, received a phone call from Ignacio Iapanaz Rebeo, Spain's junior minister for foreign affairs, thanking "the state of Qatar for its efforts in the release".

Various Spanish media, including El Pais, said the three were held by al-Qaeda's Syrian affiliate, al-Nusra Front.

LISTENING POST: Telling Syria's story - Media across the battle lines

Qatar has previously mediated the release of foreign hostages held by al-Nusra Front in Syria.

The journalists had entered Syria from Turkey on July 10 and went missing shortly afterwards, Spanish press association FAPE said last year.

According to the Syrian Observatory for Human Rights monitoring group, the three reporters were last seen in a rebel-held area of Aleppo on July 13, when they were travelling in a van together before being taken away by armed men.

After they disappeared, Spain said officials were working with Spanish intelligence members in Syria to try to secure their release.