Dozens of Turkish nationals held hostage by Islamic State jihadists in northern Iraq for more than three months have been released and brought to Turkey, Turkish Prime Minister Ahmet Davutoglu said on Saturday.

"Early in the morning our citizens were handed over to us and we brought them back into our country. At 5:00 am (0200 GMT) they entered the country," Davutoglu told reporters during an official visit to Azerbaijan, adding that all were in good health.

IS jihadists kidnapped 49 Turks including diplomats, children and special forces from the Turkish consulate in Mosul on June 11 as they captured swathes of northern Iraq.

Davutoglu said he was cutting short his Baku trip to meet the hostages in the southern Turkish city of Sanliurfa near the Syrian border.

Television footage showed a bus in Sanliurfa carrying the hostages and a motorcade accompanying them.

The circumstances of their release were not immediately clear, but President Recep Tayyip Erdogan released a written statement, saying the Turkish authorities had carried out a "pre-planned, detailed and secret operation."

"It continued all through the night and was successfully completed in the early morning. From the very first day, our intelligence agency has followed the issue with patience and determination and finally carried out a successful rescue operation."

Turkish Foreign Minister Mevlut Cavusoglu told private Haberturk television that the hostages had been brought to Turkey via the Syrian border.

"We have started the day with great news. Hope we will never experience something like this again."

On his Twitter account, he thanked "all those who contributed to the release of the hostages," especially the spy chief Hakan Fidan.

Last month, the Taraf daily reported that Ankara was in talks with the IS to hand over a historic tomb it controls in Syria in exchange for the hostages. The foreign ministry denied the report.

As it tried to gain control of the area, the IS has in the past threatened to attack the Tomb of Suleyman Shah, which Turkey controls as a sovereign exclave located in the province of Aleppo, 25 kilometres (15 miles) from the Turkey-Syria border.

The Islamic State had also kidnapped 31 Turkish truck drivers in early June in Mosul and had released them a month later.

The kidnappings had become an embarrassment for Turkey, which had imposed a media blackout on coverage of the hostage crisis.

Turkey, a NATO member and Washington's key ally in the region, has been reluctant to take part in combat operations against Islamic State militants, or allow a US-led coalition to use its airbases for strikes against the jihadists, citing its concern over for the safety of the hostages.

Ankara has been criticised for indirectly encouraging the formation of Islamic State through its support of Islamist elements within the Syrian rebellion against President Bashar al-Assad. It has rejected the criticism.

Under international pressure, Turkey in June included Al-Nusra Front -- Al-Qaeda's franchise in Syria -- and the Islamic State extremists on its list of terrorist organisations.