The European Union and the United States have called for the military junta that seized power in Niger last week to halt their coup and return President Mohamed Bazoum to office.

European Union foreign policy chief Josep Borrell on Monday expressed support for actions by the Economic Community of West African States (ECOWAS), which Sunday imposed sanctions on the coup leaders and gave them a one-week deadline to cede power or face measures including "the use of force."

Borrell said in a statement that Bazoum must be returned to power without delay. He also said the EU rejects accusations of foreign interference and that it will hold the junta responsible for any attacks on civilians or against diplomatic personnel or facilities.

U.S. Secretary of State Antony Blinken also welcomed what he called the strong leadership of ECOWAS to "defend constitutional order in Niger" and said the United States joins calls for the immediate release of Bazoum and the restoration of Niger's democratically elected government.

Blinken's spokesperson told reporters Monday that Washington has not yet made an official determination as to whether the military's actions constitute a coup, as the situation is ongoing and fluid.

"It is clear that there has been an attempt to remove President Bazoum from office," Matthew Miller told reporters. "It is not yet clear that attempt will ultimately be successful, so we are watching and monitoring the situation and trying to prevent President Bazoum from being removed from office."

Separately, a senior U.S. official told reporters that initially the mutineers did not appear to have much support from the public or senior members of the military.

"However, in subsequent conversations with some key military leaders, they've told us that they did not object to what was taking place, because they couldn't figure out how to get the presidential guard to stand down without risk to the life of the president and his family, because the presidential guard had surrounded the president's residence," the U.S. official said.

The United Nations envoy for West Africa, Leonardo Santos Simao, attended the ECOWAS summit. A U.N. spokesperson told reporters Monday that he reiterated the U.N.'s condemnation of the seizure of power by force and the undermining of democratic governance, peace and stability in Niger. He said aid deliveries continue. More than 4 million people in the country require humanitarian assistance.

Leaders of the coup have said they acted last week in response to what they described as a worsening security situation and the government's lack of action against jihadists.

In a statement on state television Monday, the military junta accused former colonial ruler, France, of planning to use military action to free Bazoum.

On Sunday, hundreds of coup supporters attacked the French Embassy in Niamey, breaking windows and burning the French flag. French officials disputed accusations from some Nigerien military leaders, saying Monday that "no lethal resources were used by the French security forces" during the embassy attack.

Margaret Besheer at the United Nations and Nike Ching at the State Department contributed to this report. Some information for this story came from The Associated Press, Agence France-Presse and Reuters.