Three senior rebel commanders were among 25 fighters killed, said the Britain-based monitor.
The Britain-based Syrian Observatory for Human Rights said that Col. Nadim al-Hassan, who heads a brigade known as “Division 30,” was picked up near the border town of Azaz along with the other six.
The move further embroils Turkey, a key NATO ally, in Syria’s civil war, and also catapults it into a front-line position in the global war against IS.
NATO itself is not involved in operations against the Islamic State group, although many of its members are. As an alliance, however, NATO is committed to helping defend Turkey.
Turkish warplanes have struck Islamic State group targets across the border in Syria.
Turkey, a NATO ally and onetime close US partner, has resisted getting embroiled too deeply in the US-led fight against Islamic State until now.
Justice Minister Rafael Catala told Spain’s Cadena SER radio on Wednesday that the government had no news regarding the three missing journalists.
Elsa Gonzalez, the president of the Spanish journalism association, told Spanish National Television that the three disappeared while working in the Aleppo area.
An anti-Islamic State group called Raqqa is Being Silently Slaughtered and the Britain-based Syrian Observatory for Human Rights said the leaflets had drawings showing dead extremists and their flag turned upside down.
Most of the prisoners in Syrian jails being prosecuted under “anti-terror” laws are opponents of the Syrian government or those who have taken part in the uprising that began in March 2011.
From Syria to Afghanistan, all you need to know about the week that was
The capture of Palmyra has raised concern that the Islamic State militants might try to destroy one of the Mideast’s most spectacular archaeological sites.
Civilians were also killed Al-Nusra Front members while worshipping in the mosque.
US said al-Harzi’s death will hurt the Islamic State’s ability to move foreign fighters in and out of the region.
Affiliations to extremist groups, lack of required mindset and other flaws continue to plague the US plan to train and arm thousands of Syrian rebels to fight the Islamic State.