“We specifically urge elements of the presidential guard to release President Bazoum from detention and refrain from violence,” Sullivan said in a statement. The White House was monitoring the situation to ensure the safety of US citizens, he added.

Presidential guards were holding the Niger president inside his palace in Niamey, the capital, on Wednesday in what neighbouring countries called an attempted coup, but which the presidency described as an “anti-republican” movement “in vain.”

White House national security spokesman John Kirby told reporters that for now there were no discussions on evacuations of Americans from Niger and said the US was still gathering details about the evolving situation.

“It’s not entirely clear what’s going on,” Kirby said. The US would not make any conclusions yet if it considered it a coup attempt, he said in response to a question, adding, “We’ll just have to watch and see where it goes.”

The US state department said it was in communication with the US embassy in Niamey.

West Africa’s main regional and economic bloc, Ecowas, said it was concerned about an attempted coup d’etat and called on the plotters to free Bazoum. The African Union also condemned what it called a coup attempt and urged the “felon” soldiers involved to return to barracks immediately.

The national army was ready to attack the guards if they did not come to their senses, the presidency said in a statement.

The US says it has spent around US$500 million since 2012 to help Niger boost its security.

“We welcome the strong statements and steps taken by the Economic Community of West African States and the African Union to defend Niger’s democracy,” Sullivan said on Wednesday.