Al Mayadin is southeast of Dayr Az Zawr in the Euphrates River Valley.
Thomas described Uzbeki as "a close associate" of al-Baghdadi who "was known to interact with him in various ways over time." Centcom has confirmed over the past two weeks that Uzbeki was killed in the raid.
The spokesman described him as facilitating the movement of ISIS foreign terror fighters and funds. Uzbeki played a key role in ISIS external terror attack plotting and Thomas said he was "clearly linked" to the deadly Istanbul nightclub shooting attack on New Year's Eve.
That deadly attack was carried out by Abdulkadir Masharipov, an Uzbeki national, on behalf of ISIS.
Masharipov fired on hundreds of revelers at the trendy Reina nightclub killing 39 people and injuring dozens of others before he fled the scene. He was captured in a police raid in Istanbul two weeks after the attack and, according to Turkish authorities, confessed to his role in the attack.
Uzbeki is believed to have been involved in planning the attack.
Thomas described the April 6 ground raid in Syria targeting Uzbeki "as an operation in order to eliminate him." The raid was conducted by American special operations forces, said a defense official.
Since late 2015 an "expeditionary targeting force" has operated inside Iraq and Syria targeting senior ISIS leaders. Typically their ground operations are not disclosed.
"We have a campaign against leaders of ISIS and a campaign against the leaders of al-Qaeda," said Thomas. "You can kind of look through the history of the strikes and I think we have a pretty good record of finding these folks and killing them."
Uzbeki's presence in al Mayadin seems to reinforce information from U.S. officials that senior ISIS leaders have escaped Raqqa, the de facto ISIS capital in Syria, heading towards areas of the Euphrates River Valley.
Senior ISIS leaders have also departed Mosul into the same valley region, which straddles both sides of the border, according to U.S. officials.