Turkish Prime Minister Recep Tayyip Erdoğan is set to hold a “lengthy” meeting with U.S. President Barack Obama in Seoul on March 25, and the issue of Turkey’s oil imports from Iran is expected to be high on the agenda, sources say.

According to Hurriyet Daily News, the two leaders, scheduled to meet on the eve of the Nuclear Security Summit in the South Korean capital, will discuss a wide range of issues, including the turmoil in Syria. The timing of the talks is critical: From Seoul Erdoğan will travel on to Tehran for talks with Iran’s top leaders on March 28-29, and the Friends of Syria Group will convene in Istanbul on April 1.

“I expect it to be a comprehensive and lengthy meeting. That’s why it has been fixed not for the sidelines of the summit but a day ahead of it,” an aide to Erdoğan said.

Erdoğan will discuss Turkey’s oil imports from Iran, which will become subject to U.S. sanctions after June 28, with both Obama and with the Iranian leadership, Energy Minister Taner Yıldız said.