Nigeria, the current chair of Ecowas, has vowed a firm line against coups that have proliferated across the region since 2020.
West Africa's regional bloc on Wednesday said a military intervention in junta-ruled Niger was "the last resort" as Nigeria cut electricity supplies to intensify pressure on the country's coup leaders.
As ex-colonial power France sent in a fifth plane to evacuate its citizens, coup leader General Abdourahamane Tiani insisted they had no reason to quit the country.
Joining the departures, the United States ordered a partial evacuation of its embassy in Niamey.
West African military chiefs were meeting in Nigeria's capital Abuja to frame a response while a delegation was in Niger for negotiations, a week after the coup that shook the fragile nation.
Economic Community of West African States (Ecowas) leaders on Sunday imposed trade and financial sanctions, giving the coup leaders a week to reinstate Niger's democratically elected president or face the possible use of force.
"(The) military option is the very last option on the table, the last resort, but we have to prepare for the eventuality," said Abdel-Fatau Musah, Ecowas commissioner for political affairs, peace and security.
An Ecowas team headed by former Nigerian leader Abdulsalami Abubakar was in Niger for talks, he added at the start of a three-day meeting of the grouping's military chiefs in Abuja.
West Africa's pre-eminent military and economic power Nigeria, the current chair of Ecowas, has vowed a firm line against coups that have proliferated across the region since 2020.
A source in Niger's power company, Nigelec, said Nigeria had cut electricity to its neighbour as a result of the sanctions.
Niger, one of the world's poorest countries, depends on Nigeria for 70 percent of its power.
Junta-ruled Mali and Burkina Faso have warned any military intervention in their neighbour would be tantamount to a "declaration of war" against them.
General Salifou Mody, one of the Niger coup leaders, arrived with a delegation in Mali's capital Bamako on Wednesday. In an interview broadcast on Malian state television that evening, he stressed the need for cooperation between the two countries.
Russia on Wednesday called for "urgent national dialogue" in Niger and warned that threats of intervention "will not help ease tensions or calm the domestic situation".
Later Wednesday, the World Bank became the latest international organisation to announce it was suspending aid to Niger "other than private sector partnerships".
President Mohamed Bazoum, 63, was feted in 2021 after winning elections that ushered in Niger's first-ever peaceful transition of power.
He took the helm of a country burdened by four previous coups since independence from France in 1960.
But after surviving two attempted putsches, Bazoum was overthrown on July 26 when members of his own guard detained him at the presidency.
Their commander, General Tiani, has declared himself leader, but his claim has been condemned internationally.
France organised evacuation flights from Niamey following hostile demonstrations at the weekend.
But in a televised address Wednesday, Tiani said French nationals had nothing to fear, insisting they had never been subject "to the least threat".
He rejected the international sanctions imposed in response to the coup, saying he "refused to give in to any threat".
"By Wednesday, French planes had evacuated 992 people, 560 of them French citizens," said Paris.
"The same day, the US State Department ordered the departure of non-emergency US government employees and eligible family members from Embassy Niamey," it said in a statement.
Italy's foreign ministry said it had evacuated 68 civilians, including Italians and other nationals living in Niger, who arrived in Rome early Wednesday.
Eighteen Italian soldiers were also on the flight.
Germany has urged its citizens to leave, but the United States -- which has 1,100 troops stationed in Niger -- has opted to not evacuate Americans for now.
Under Bazoum and his predecessor Mahamadou Issoufou, Niger has had a key role in French and Western strategies to combat a militia insurgency that has rampaged across the Sahel since 2012.
After joining a regional revolt in northern Mali, armed Islamists advanced into Niger and Burkina Faso in 2015 and now carry out sporadic attacks on fragile states on the Gulf of Guinea.
Countless civilians, troops and police have been killed across the region, while around 2.2 million people in Burkina Faso alone have fled their homes.
The impact has contributed to army takeovers in all three Sahel countries and inflicted devastating damage to economies at the very bottom of the world's wealth table.
France's anti-militia Burkina Faso mission had at its peak about 5,400 troops, supported by fighter jets, helicopters and drones.
But the mission was refocused on Niger last year, when France pulled out of Mali and Burkina Faso after falling out with their juntas.
Today, the reconfigured force has around 1,500 men, many of them deployed at an air base near Niamey.