REYHANLI, Turkey—A senior commander of the Islamic State (formerly the Islamic State of Iraq and Sham) has told the Washington Post that Turkey’s support was instrumental in the success of his organization, which now controls great swathes of Syria and Iraq.

In an interview with the Washington Post on Aug. 12, the 27-year-old commander identifying himself as Abu Yusef explained that the Islamic State received most of its supplies from Turkey and had many of its fighters from Syria treated at Turkish hospitals. Abu Yusef, speaking to the Washington Post in the southeaster Turkish town of Reyhanli near the Syrian border, says much of that has changed as the Turkish government has begun cracking down on IS operations.

“It is not as easy to come into Turkey anymore,” Yusuf says. “I myself had to go through smugglers to get here, but as you see, there are still ways and methods.”

“We used to have some fighters — even high-level members of the Islamic State — getting treated in Turkish hospitals. And also, most of the fighters who joined us in the beginning of the war came via Turkey, and so did our equipment and supplies,” Yusef told the Washington Post.

Turkey closed its doors on the Islamic State when the extremists took their war into Iraq, capturing 80 Turkish citizens in the process, 40 of whom are still in captivity. But now, Yusef says, the Islamic State has enough resources in Syria and Iraq that it no longer needs Turkey’s support.

The piece, authored by Anthony Faiola and Souad Mekhennet, gives an exhaustive account of Turkey’s relationship with the Islamic State. It can be read on the Washington Post’s website.