The 15-nation bloc is reconvening for its own diplomatic push on the crisis with a summit Thursday in Nigerian capital Abuja.
No agreement was reached after second-ranking US diplomat met Niger’s military leaders on Monday.
The move was to urge the coupists to reverse the coup and return the ousted President back to his position.
AFP reported no headway a day after an ultimatum from the West African bloc ECOWAS was ignored.
Victoria Nuland, a veteran envoy and acting deputy secretary of state, said she met for more than two hours with military chiefs who ousted democratically elected Western ally Mohamed Bazoum on July 26.
Nuland’s trip, conducted in secrecy until she left, came after the expiration of a deadline set by ECOWAS to reinstate Bazoum by midnight (2300 GMT) on Sunday or risk military intervention.
The 15-nation bloc is reconvening for its own diplomatic push on the crisis with a summit Thursday in Nigerian capital Abuja.
A source close to ECOWAS said an immediate military intervention to restore Bazoum was not envisaged at this stage, adding that the path to dialogue still appeared open.
Speaking to reporters before her departure, Nuland described her talks as “extremely frank and at times quite difficult”.
She said she offered the coup leaders “a number of options” to exit the crisis and restore the relationship with the United States, which like other Western nations has suspended aid.
“I would not say that we were in any way taken up on that offer,” she said.
She added that the coup leaders did not respond to her requests to meet Niger’s self-proclaimed new leader, General Abdourahamane Tiani, or the detained elected president, Mohamed Bazoum, although US officials have been in touch with Bazoum by telephone.
Nuland said she met Brigadier General Moussa Salaou Barmou, who has been named the new military chief of staff and who has worked closely in the past with the United States, which along with former colonial power France has based anti-jihadist operations in the Sahel out of Niger.
Nuland said she warned Niger against following neighbouring Mali in bringing in Russia’s Wagner mercenaries.
“The people who have taken this action here understand very well the risks to their sovereignty when Wagner is invited in,” said Nuland, who is known for her hawkish stance on Russia.