Turkey’s state intelligence agency helped deliver arms to parts of Syria under Islamist rebel control during late 2013 and early 2014, according to a prosecutor and court testimony from gendarmerie officers seen by Reuters.

The witness testimony contradicts Turkey’s denials that it sent arms to Syrian rebels and, by extension, contributed to the rise of Islamic State, now a major concern for the NATO member.

Syria and some of Turkey’s Western allies say Turkey, in its haste to see President Bashar al-Assad toppled, let fighters and arms over the border, some of whom went on to join the Islamic State militant group which has carved a self-declared caliphate out of parts of Syria and Iraq.

Ankara has denied arming Syria’s rebels or assisting hardline Islamists. Diplomats and Turkish officials say it has in recent months imposed tighter controls on its borders.