A large amount of fertilizer — a significant ingredient for explosives — is flowing from Turkey into territories held by the Islamic State in Iraq and Levant (ISIL) in Syria, amid concerns that Turkey is not doing enough to seal off ISIL’s supply lines, a report has claimed.

The New York Times quoted Mehmet Ayhan, a Turkish opposition politician, as saying, “It is not for farming. It is for bombs.” Reporters for the newspaper witnessed — four times on two recent days — large wooden carts loaded with fertilizer entering the Akçakale border gate and returning empty shortly afterwards.

The fertilizer, ammonium nitrate, is used for agricultural purposes but also by terrorist networks to build powerful explosives. Unlike the Harran and Akçakale districts, the closest Turkish towns to the border, the ISIL-held territories in Syria are dry and arid, making it essential for farmers to use fertilizer to increase productivity, particularly in the spring months.

The news report said few in Akçakale believe the fertilizer is meant to help Syrian farmers, adding that the open transportation of ammonium nitrate into ISIL territory points to “lingering questions about Turkey’s commitment to isolating its jihadist neighbors.”

Ankara has long been accused of fostering ISIL and radical groups in Syria to fight against the Syrian regime. Turkey rejects the accusations, says it is fighting a lonely battle against terrorists in Syria and that it does whatever it takes to impede the flow of foreign fighters from joining the ranks of ISIL. For nearly two months, Turkey has mostly closed all its border gates with Syria, largely because of fears that militants could slip into Turkey and target sensitive areas ahead of crucial parliamentary elections in June.

The newspaper mentioned one Turkish smuggler, now retired, who received $35 a head to move at least 25 foreign fighters for ISIL.

The New York Times said Turkish officials failed to explain why the substance was allowed to cross the border. Mustafa Güçlü, a spokesman for the Akçakale mayor’s office, first denied that any fertilizer was crossing, then said if there was any, it would be for agriculture. One official at the border crossing reportedly said that about 500 Syrians returned home every few days and that each was allowed 30 or 40 bags of low-nitrate fertilizer, “which is less explosive,” the report cited Mustafa Kurt, a café owner, as saying. “Of course they use it to make bombs.”