No group has claimed responsibility for the Thursday attack.
The former defence minister, Sadio Camara, was killed in coordinated terrorist attacks on April 25.
The Malian military said on Saturday that fighting is still ongoing
The operation took place on Friday in north-western Syria, CENTCOM said.
Messrs Usman and Abba, popularly called Mallam Mamuda, were arraigned on 32-count charge bordering on terrorism and others.
“He comes from a very tough place, and he’s a tough guy. I like him,” said Mr Trump, heaping praise on Mr al-Sharaa.
“The failure of successive governments in Nigeria to prevent, arrest, or punish perpetrators decisively created room for several conspiracy theories,” said Mr Dickson.
The Nigerien security authorities are said to be conducting a nationwide search.
Information minister Mohammed Idris commended the military and other security forces for their collaborative efforts.
U.S. President Donald Trump met with Syrian President Ahmed al-Sharaa in Riyadh on Wednesday, a U.S. government representative confirmed.
