Monitors in northern Syria reported fierce fighting Sunday between Islamic State fighters and U.S.-backed Kurdish units at an airbase about 50 kilometers from the jihadists' de facto capital, Raqqa.
The Syrian Observatory for Human Rights and several other regional media reports are calling the fighting the "Battle for Tabqa," a key Euphrates River town downstream from Raqqa.
Details were sketchy late Sunday, but the pro-government news outlet al-Masdar said stiffened IS resistance included a suicide attack that killed at least 15 Kurdish fighters near the al-Tabqa dam. The report said the Kurdish force nonetheless had repelled the IS attack early Sunday.
Al-Masdar also reported that jihadist infighting erupted Saturday in nearby Tabqa city over apparent disagreements on whether extremist fighters should surrender.
Neither report has been independently confirmed. However, if verified, they would coincide with U.S.-led coalition airstrikes Saturday that killed at least five people and wounded an unknown number of others near Tabqa city.
Anti-IS offensive gathering steam
Analysts describe Tabqa as the last fortified line of defense for Islamic State fighters seeking to defend western Raqqa from a gathering anti-jihadist offensive.
The anti-jihadist forces, led by U.S.-backed Kurds and a separate, largely Syrian Arab militia, have been pushing toward Raqqa for weeks, and are expected to launch coordinated attacks on the city later this year.
In a separate development Saturday, Israeli airstrikes targeted a Syrian base near the northern Israeli border that Israel says housed a militia group loyal to embattled Syrian President Bashar al-Assad.
An Israeli military statement said the strikes early Sunday in Syria's Quneitra province came in response to Syrian artillery shells that allegedly landed late last week in the Golan Heights - a strategic Syrian plateau bordering Israel seized by the Jewish state in the Six-Day War of 1967.
There were no reports of casualties in either exchange.