According to the Syrian Observatory for Human Rights, 42 people were killed in the airstrike, which took place on Monday at dawn.
The worldwide coalition began its military campaign in Syria on September 23, 2014, nearly three months after the extremists proclaimed a caliphate in Syria and Iraq.
"The coalition conducted strikes on known Isis command and control facilities and other Isis infrastructure in Mayadin, Syria, June 25 and 26", a spokesman for the US-led coalition told Newsweek.
Along with the Syrian Democratic Forces, led by Kurdish militias, the coalition is now taking part in an offensive against IS positions in al-Raqqa province, the terror organization's main stronghold in Syria.
Dillon added that Observatory reporting had previously been exaggerated.
"So, ISIS is forcing civilians to stay in and around such headquarters to cause as many civilian casualties as possible in the strikes", he said.
It was not immediately clear how either the Observatory or Deir Ezzour 24 identified the aircraft responsible for the strike.
Syrian state-run TV station al-Ikhbariya also cited a correspondent in the area as saying thatcoalition warplanes had destroyed a building in al-Mayadeen used as a prison by IS.
Mayadeen lies in the Euphrates Valley some 45km southeast of the provincial capital of Deir Ezzor.
Among operations moved to al-Mayadeen, about 80 km (50 miles) west of the Iraqi border, are its online propaganda operation and its limited command and control of attacks in Europe and elsewhere, they say.