Washington is "certainly aware of efforts by France and other European nations to evacuate their citizens. At the same time, we don't have any indications of direct threats to US citizens or to our facilities, so we have not changed our posture with respect to our presence in Niger at this time," National Security Council spokesman John Kirby said.

About 1,000 US troops are stationed in the land-locked African nation, where they were helping the ousted president, Mohamed Bazoum, combat a regional Islamist insurgency.

Kirby said the White House still sees a "window" for diplomacy to resolve the Niger crisis but added that "we're monitoring it literally by the hour."

"We do continue to urge American citizens that are in Niger to make sure safety is their first priority," he said.

Kirby also said the US military in Niger was not taking part in the European airlifts.

"There's been no decision to use them in any way to support evacuation efforts by other countries," he said, and there has been "no decision made about pre-positioning any additional forces in or nearby."

"If we have to make adjustments, we'll make adjustments," he said. "We're just not there."

Pentagon spokesman Brigadier General Pat Ryder said American forces have curtailed certain activities in Niger.

"As far as security cooperation, those efforts right now are suspended in light of the situation," he said, later specifying that this includes "training, for example, those types of things."

Ryder also said American troops in Niger are largely staying on military bases, though they are still going outside "to engage with our Nigerien counterparts as necessary."

"Our focus right now is on making sure that our troops continue to stay safe," he said.