Two US Army soldiers and three members of the Kurdish-led forces were killed in a car bomb attack in the town of Granij in eastern Deir ez-Zor province, activists said Wednesday.
An Islamic State (ISIS) car bomb rocked a joint US and Syrian Democratic Forces (SDF) military convoy, according to activist Taj al-Allow.
Three civilians were also killed in an ISIS rocket attack on the SDF-held town of al-Ja'abi.
In retaliation, the International Coalition launched heavy airstrikes on the ISIS pockets.
Since Tuesday, clashes have intensified between the SDF and ISIS in eastern Deir ez-Zor province as the YPG-led fighters press to uproot the militants from their last pockets near the Iraqi border.
The fighting took place in the village of al-Safafneh near the strategic Bagouz area, a key ISIS stronghold on the eastern bank of Euphrates River.
The SDF seized control of al-Shajlah village last week and half of the village of Bagouz.
The Kurdish-led forces have been among the most effective in the fight against ISIS in Syria, forcing them out of much of the country's east.
Over the course of just two weeks, at least 16 SDF fighters were killed in ISIS attacks on their checkpoints in eastern Deir ez-Zor. In turn, the SDF has killed at least 40 ISIS militants.
Despite losing most of the territory it held between Iraq and Syria since its peak in 2014, ISIS remains a disruptive force in both countries. Its leader, Abou Bakr al-Baghdadi, urged his followers to "persevere" in an audiotape attributed to him last month.
On Monday, ISIS territory also came under missile attack by Iran's Revolutionary Guards who struck its headquarters in retaliation for an attack that killed 24 people in the Iranian city of Ahvaz.
The Iranian Revolutionary Guard released pictures of what appeared to be missiles lighting up the night sky, leaving trails of smoke as they soared above a desert region with a rugged mountain in the background.
The missiles hit the desert border town of Albu Kamal on the Iraqi border.
This article was edited by The Syrian Observer. Responsibility for the information and views set out in this article lies entirely with the author.