Syrian activists and Kurdish officials say a German woman fighting alongside Kurdish militiamen has been killed in a battle against the ISIS terror group.

They say Ivana Hoffman, a native of South Africa with German citizenship, was killed Saturday while fighting alongside the Kurdish Peoples Protection Units, known as the YPG.

YPG spokesman Nawaf Khalil said Monday that Hoffman was killed near the Syrian village of Tel Tamr. Hoffman was a member of the Marxist-Leninist Communist Party in Turkey.

Serdar Sitr, president of the Kurdish Solution Party in Iraq, and the Britain-based Syrian Observatory for Human Rights also confirmed Hoffman's death.

Hoffman is the third foreign national -- and the first female foreign fighter -- known to be killed fighting with Kurdish forces against the Islamic State group.

Earlier Monday, activists claimed that airstrikes by the U.S.-led coalition hit a Syrian oil refinery held by ISIS.

The strikes targeted a refinery near the Turkish-Syrian border outside the town of Tel Abyad. Video from the Turkish Dogan News Agency showed the strikes Sunday night, which saw an enormous fireball engulf the refinery.

The Syrian Observatory for Human Rights estimated the strikes killed about 30 people, including ISIS militants and refinery workers. The Syrian activist group Raqqa is Being Slaughtered Silently also reported the strikes, but offered no casualty figure.

ISIS, which controls a self-declared caliphate on captured territory covering about a third of Syria and Iraq, partially funds its conquests through the sale of black market oil.

The coalition did not immediately acknowledge launching the strike.