The group of West African delegates arrived in the Nigerien capital of Niamey on Saturday.
The coup leaders rejected the regional bloc's demands to reinstate ousted Nigerien President Mohamed Bazoum, Al Arabiya reported.
On Saturday, French state broadcaster RFI reported that the delegation visited Niger's deposed president to assess conditions of his detention. Later in the day, the British media reported that the delegation also held talks with Gen. Abdourahmane Tchiani, head of the rebel-run transitional government.
A coup took place in Niger on July 26. Bazoum was ousted and detained by his own guard, led by Tchiani. Following the coup, ECOWAS suspended all financial aid to Niger, froze rebels' assets and imposed a ban on commercial flights to and from the country.
In early August, during a summit in the Nigerian capital of Abuja, ECOWAS leaders agreed to activate a standby force to potentially compel the Nigerien military to reinstate Bazoum. On Friday, ECOWAS Commissioner for Political Affairs Abdel-Fatau Musah said that ECOWAS general staff chiefs had agreed on a date for the beginning of military intervention, but would not make it public.