At a meeting between officials from the U.S. and Niger in Niamey, the county’s capital, on Monday, a U.S. ally and a top Nigerien general involved in the coup declined to guarantee the safety of President Mohamed Bazoum, now being detained by the rebels, leaving some U.S. officials concerned Bazoum could be in danger.

Acting Secretary of State Victoria Nuland traveled to Niger on Monday with the hope of meeting with Bazoum, the democratically elected president toppled in the coup, and the new self-proclaimed leader of Niger, Gen. Abdourahmane Tchiani. Nigerien officials blocked both meetings.

Nuland, along with U.S. diplomatic and military officials instead met with the junta’s chief of defense, Gen. Moussa Salaou Barmou, who has led the Nigerien Special Forces for the past decade. He was trained by American forces and worked closely with U.S. military leaders and troops assigned to train and support Nigerien Special Forces with intelligence collection in their fight against Islamic extremist groups.

The Americans met with the defense chief and others from the new junta for more than two hours and Nuland described the conversation as “quite difficult” at times.

Officials familiar with the discussions said the military junta made it clear to Nuland and the other U.S. officials present that they believe very strongly that their seizure of power was just, that they have broad public support, and that Bazoum is no longer the legitimate leader of Niger. Barmou also made it clear that the coup leaders will not release Bazoum from house detention and that he will not be returned to power, the officials said. Barmou also did not guarantee Bazoum’s safety, especially if outside military forces intervene in Niger, two of the officials said.

Secretary of State Antony Blinken spoke with Bazoum on Tuesday afternoon and State Department officials on Wednesday again called on coup leaders to protect him.

“We are deeply concerned about the welfare of President Bazoum and his family, and the deteriorating conditions of their detention,” said State Department spokesperson Matt Miller. “As we have since the beginning of this situation, in both public and private communications, the United States continues to raise the importance of President Bazoum and his family’s well-being and safety. We reiterate our calls for their immediate release.”

“[N]uland also met with NGO leaders and others from civil society,” Miller told NBC News. “She heard very clearly from them that they are deeply concerned about the situation. … [I]t’s clear there are many people who aren’t going to stadiums and marching in the streets the way you see so-called supporters of the junta doing because they have very real concerns about their safety if they do so. But their support for democracy is very much real.”

A U.S. official who asked not to be named said that the coup leaders appear increasingly defiant. “The junta appears to be fairly dug in,” the official said. “There is no indication of them being willing to compromise right now. In fact, they are becoming harder in their views.”

Several U.S. officials agreed that while there is still some hope for diplomacy, it is fading. “There’s no keen sense of optimism after the meeting,” one official said.

American officials say they are not yet leaning toward formally declaring this a coup, which would under U.S. law trigger a halt to training and hundreds of millions of dollars in aid to Niger. The U.S. military support in the country gives Washington a bargaining chip, because the coup leaders told U.S. officials they want to keep it.