Iraqi F-16 fighter jets carried out a "successful strike targeting a meeting of Daesh (IS) leaders" on Friday in the Hajin region, in the eastern Syrian province of Deir Ezzor, a military statement said.
Among those killed, it said, were a senior member of the jihadists' "ministry of war", his deputy, a local commander and a media official. There was no independent confirmation.
Three houses linked by an underground tunnel were also destroyed, it said, adding that the air strike was carried out based on "intelligence" and at the request of Prime Minister Haider al-Abadi.
Hajin, about 50 kilometres (30 miles) from Iraq's border, is the largest populated hub still under IS control in Syria.
Last month the Britain-based Syrian Observatory for Human Rights that monitors the Syrian war said that at least 65 senior IS members live in Hajin.
The town has been surrounded since the end of last year by the Syrian Democratic Forces, a US-backed alliance of Kurdish and Arab fighters, the monitor says.
Iraq's air force has carried out several strikes on IS-held territory in Syria since April, including one targeting "the headquarters of IS terrorist gang leaders" in Hajin on May 24.
The following day Iraq released a video showing a strike on a huge building surrounded by palm trees and a wall which then collapsed.
IS declared a cross-border "caliphate" in Syria and Iraq in 2014, seizing a third of Iraq during a sweeping offensive.
The jihadists have since lost much ground to separate counter-offensives by Syrian and Iraqi forces as well as US-led operations, and the jihadist presence has been confined to a few holdouts in Deir Ezzor.
In December the Iraqi government declared victory over IS but the military has continued regular operations targeting mostly desert areas along the porous Syrian border.
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