U.S. President Donald Trump said that Iran’s Supreme Leader Ali Khamenei “should be very worried,” while Iranian Deputy Foreign Minister Abbas Araghchi clarified that nuclear talks with the United States will be held on Friday in Muscat. The negotiations face the risk of collapse after disagreements over the venue and format, but both sides have affirmed their commitment to meet despite disputes over the issues on the table.

Trump told NBC News, “I can say he should be very worried, yes, he should be. And as you know, they are negotiating with us.”

Trump’s remarks come as the United States increases its military presence in the region, coinciding with preparations by Washington and Tehran to hold nuclear talks next Friday.

Earlier on Wednesday, U.S. reports revealed that the nuclear negotiation track between Washington and Tehran is at risk of collapsing after the United States rejected Iranian demands to change the location and format of the planned Friday talks—a development that deepens disagreements and threatens to close the window for a diplomatic solution.

However, Iranian Deputy Foreign Minister Abbas Araghchi confirmed Wednesday evening that “the nuclear talks with the United States will be held at 10 a.m. on Friday in Muscat.”

A U.S. official also confirmed this to Reuters, saying, “The U.S.-Iranian talks will be held in Oman on Friday.”

Iran and the United States had agreed to hold a meeting on Friday in Istanbul, with other countries participating as observers.

But Tehran expressed its desire to move the talks to Oman and hold them in a bilateral format, limiting the discussion to the nuclear file and excluding other issues such as ballistic missiles, which remain a priority for Washington and regional states.