West African leaders on Sunday threatened military action against Niger, where soldiers seized power in a coup on Wednesday, unless the country’s democratically elected president was restored to office within a week.

The demand was issued by the Economic Community of West African States, or ECOWAS, the 15-member regional bloc, after a crisis summit meeting in Nigeria. It echoed earlier calls by the United States and France, major security allies of Niger, threatening to cut aid and military ties unless the deposed president, Mohamed Bazoum, was restored.

After coup supporters massed on Sunday outside the French Embassy in the capital, Niamey, calling for the withdrawal of French troops, President Emmanuel Macron issued a stiffly worded warning. Any attack on France’s citizens or interests in Niger would be met with an “immediate and uncompromising” reaction, Mr. Macron said in a statement.

ECOWAS, in a statement, vowed to take “all measures necessary” to restore democratic rule in Niger and said that “may include the use of force.” It imposed financial sanctions on the putschists, led by the new self-declared leader, Gen. Abdourahmane Tchiani.

The newly installed junta, however, insisted it was going nowhere. In a statement before the summit, it warned forcefully against any foreign military intervention.

“We want to once more remind ECOWAS or any other adventurer of our firm determination to defend our homeland,” a junta spokesman said on Saturday night in a televised statement.

The summits and dueling statements fueled the growing sense of crisis in Niger, a vast and impoverished country where the coup caught many by surprise, including Western countries now seeking to engineer a reverse.

That is a tall order: Experts say coups are very hard to overturn once a few days have passed. But the demands are a measure of the alarmed response to the turmoil in a country seen by the West as a crucial ally in a region where Islamist militants are expanding their grip.

France has about 1,500 troops in Niger, which it ruled as a colony until 1960, and there are about 1,100 American troops, many stationed at drone bases used to carry out airstrikes against militants in Niger and neighboring countries.

On Saturday, France and the European Union suspended some aid to Niger, and the U.S. secretary of state, Antony J. Blinken, said that American security ties, worth about $500 million since 2012, were also in jeopardy.

As ever in the region these days, Russia loomed in the background.

Coup supporters waved Russian flags in Niamey on Sunday and hung one on the wall of the French Embassy — an echo of similar scenes in Burkina Faso and Mali, where Russian flags also emerged among people celebrating coups in 2021 and 2022.

Experts say there is no evidence that Russia is behind the coup in Niger, where personal factors are considered a more probable trigger. Tensions had been building steadily between Mr. Bazoum and the head of the presidential guard, General Tchiani.

(Mr. Bazoum’s whereabouts remained uncertain on Sunday, although he was widely presumed to still be in detention at the presidential palace.)

Still, experts say it’s another sign of how Russia has positioned itself as the emblem of anti-Western, and especially anti-French, sentiment in broad patches of Africa. And that helps to create other openings for the Kremlin.

In neighboring Mali, about 1,000 paramilitaries from Russia’s Wagner private military company have replaced about 5,000 French troops who pulled out last year. Wagner is also a major presence in the Central African Republic, where it protects President Faustin-Archange Touadéra, who held a referendum on Sunday aimed at prolonging his tenure.

The coup in Niger means that an uninterrupted line of countries stretching across Africa, from the Atlantic to the Red Sea, is under military control. Many are former French colonies where a visceral anger at perceived French paternalism and post-colonial meddling has boosted support for the putschists.

“Niger has suffered too much under France’s orders,” said Karimou Sidi, a pro-coup demonstrator in Niamey on Sunday. “Enough is enough.”

The coups are straining traditional regional blocs, like ECOWAS, which in recent years has suspended three of its states — Burkina Faso, Guinea and Mali — over military coups, with Niger possibly following soon.

In recent decades, ECOWAS has deployed peacekeepers to numerous crisis-hit countries, including Liberia and Guinea-Bissau. Despite its tough talk on Sunday, it may need to find a middle path to navigate its way out of the Niger crisis, said Idayat Hassan, a Nigerian analyst.

“Any strong sanctions will impact citizens the most in a country and region with increasingly strong anti-West sentiments, while also pushing the putschists more into the hands of Russia and or Prigozhin and Wagner forces,” Ms. Hassan, a senior associate with the Center for Strategic and International Studies, a Washington-based research institute, said, referring to Yevgeny V. Prigozhin, who leads the mercenary group.

Omar Hama Saley contributed reporting from Niamey, Niger, and Elian Peltier from Abidjan, Ivory Coast.