Saudi Crown Prince Mohammed bin Salman has sent a letter to the United Arab Emirates’ National Security Adviser Tahnoon bin Zayed, expressing concerns about Abu Dhabi’s policies in Yemen and Sudan. The letter, sent several weeks ago, raised allegations regarding the UAE’s activities in both conflict zones, according to Middle East Eye citing multiple U.S. and Western officials.

In the message, the Saudi Crown Prince reportedly described Riyadh’s military involvement in Yemen as necessary for national security and indicated that Saudi Arabia views Yemen as part of its sphere of influence. The letter also proposed mediation through Prince Khalid bin Salman, the Saudi defense minister and brother of the Crown Prince.

Neither Saudi Arabia nor the United Arab Emirates has publicly commented on the report, which was first published by Middle East Monitor.