Members of the al-Qaeda-linked group also fought against Kurds around the town of Ras al-Ain, said a Kurdish activist, Bassam al-Ahmed.
According to opposition sources, 14 al-Qaeda-linked militants and four Kurdish gunmen were killed in the clashes.
An FSA member, who identified himself as Abu Raed, also said a soldier from the Northern Storm brigade, which is part of the foreign-backed group, was killed in Azaz.
Syria has been gripped by deadly unrest since 2011. According to reports, the Western powers and their regional allies — especially Qatar, Saudi Arabia, and Turkey — are supporting the militants operating inside Syria.
In a recent statement, the United Nations High Commissioner for Refugees said the number of Syrian refugees, who have fled the 30-month-long conflict, reached two million.
The UN refugee agency also said some 4.2 million people have also been displaced inside Syria since the beginning of the conflict in the Arab country.