Nigerien Defence Minister Kalla Moutari, US ambassador Eunice Reddick and other lawmakers watched as the four bodies were taken from the city morgue in Niamey, before being buried in a cemetery.
With tears in their eyes, the widows, children and relatives of those killed also took part in the ceremony, during which Nigerien soldiers praised their fallen comrades for their “dynamism” and “bravery” in the fight against “terrorists”.
“We will never forget you,” they said, adding that “the entire nation expresses its heartfelt gratitude for the sacrifice made”.
A joint US-Nigerien patrol came under fire on Wednesday in southwestern Niger near the border with Mali, where Islamic State jihadists have established a presence.
According to Radio France Internationale, the ambush took place after militants from Mali attacked the village of Tongo Tongo in Tillaberi.
A counter-operation was launched, but the American and Niger soldiers fell into a trap, RFI reported.
The Pentagon said the clash took place approximately 200 kilometres (120 miles) north of Niamey.
Niger’s President Mahamadou Issoufou said Thursday the fatal ambush was the latest attack on his country by “terrorist groups”.
Eight Nigerien soldiers were wounded in the attack, which also killed three US Green Berets and a fourth soldier. US Africa Command said two more Special Forces troops were wounded.
Issoufou convened a special National Security Council meeting after the attack to “assess” the country’s security apparatus and met with Reddick, according to media reports.
The clash proved the first confirmation of the little-known presence of US troops in the turbulent area, part of the poor and politically fragile Sahel where jihadist groups are mounting an insurgency.
US troops have increased their presence in Niger in recent years but this appeared to be their first firefight, Lieutenant General Kenneth McKenzie, Joint Staff Director, told reporters in Washington on Thursday.
Under the name Operation Barkhane, France also maintains a 4,000-man mission in the region to shore up fragile Sahel countries against jihadists who have carried out a wave of bloody bombings, shootings and kidnappings.
Niger on Friday declared three days of national mourning.