BEIRUT - The international fight against the Islamic State of Iraq and Syria (ISIS) flared up on several fronts over the past 24 hours, with reports emerging from Syria of a German woman killed fighting against the militants and an airstrike by the U.S.-led coalition destroying an oil refinery in ISIS-controlled territory. In Iraq, meanwhile, ISIS is trying to fend off an offensive by government troops and Shiite militias against the central city of Tikrit, while new details emerged about an attack by ISIS-affiliated militants in Libya.

Here's a look at the latest developments:

GERMAN WOMAN KILLED FIGHTING WITH KURDS AGAINST ISIS

A German woman fighting with Kurdish militiamen was killed during heavy fighting with ISIS in northwestern Syria, officials said Monday, becoming the third known Westerner to be killed after taking up arms with Kurdish forces battling the extremist militants.

Ivana Hoffmann, 19, died Saturday while fighting in the ranks of the Kurdish Peoples Protection Units, known as the YPG, near the Syrian village of Tel Tamr in Hassakeh province. Hoffmann, born in Germany to South African parents, was a member of the Marxist-Leninist Communist Party (MLKP) in Turkey and joined YPG fighters about six months ago, the party said in a statement. It referred to Hoffmann by her nom de guerre, Avashin Tekoshin, and said she died in pre-dawn clashes with ISIS on Saturday.

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A video posted early Monday morning on a Facebook page memorializing Hoffmann shows a woman with her face covered by a scarf holding a weapon. "I decided to come to Rojava because they are fighting for humanity here, for rights and for internationalism that the MLKP represents," she said in German, referring to the now largely autonomous areas in north and north-eastern Syria run by Kurds. "We are here as the MLKP to fight for freedom. Rojava is the beginning. Rojava is hope."

German authorities say some 650 people have traveled from Germany to Syria and Iraq, to join Islamist groups, but they haven't said how many are estimated to have joined Kurdish or Christian groups opposing ISIS.

US-LED COALITION AIRSTRIKES HIT ISIS-HELD OIL REFINERY

Coalition warplanes bombed a refinery near the Syrian town of Tel Abyad on the Turkish border late Sunday, lighting up the night sky with an enormous fireball, activists said. The Britain-based Syrian Observatory for Human Rights said the strikes killed some 30 people.

The U.S. military's Central Command said in a statement Monday that coalition aircraft struck an ISIS "modular oil refinery" near the town of Kobani on the Turkish border. Kobani is 30 miles from Tel Abyad.

ISIS, which controls about a third of Syria and Iraq, sells black-market oil to help fund its conquests, making makeshift refineries and other fuel-related facilities in ISIS-held territory frequent targets for coalition jets.

IRAQI GOVERNMENT PRESSES OFFENSIVE AGAINST TIKRIT ISIS MILITANTS

Iraqi government troops and Shiite militias forged ahead with their offensive to retake Saddam Hussein's hometown of Tikrit from Islamic State militants. The operation, which is taking place without assistance from the United States, has clawed back a few villages and towns since it began last week, most notably Dawr, south of Tikrit.

Directing the offensive with the aid of dozens of Iranian military advisers is a powerful Iranian general, Ghasem Soleimani, commander of the powerful Revolutionary Guard's Quds Force. The overt Iranian role and the prominence of Shiite militias in the campaign have raised fears of possible sectarian cleansing should Tikrit, an overwhelmingly Sunni city, fall.

On Monday, Iraqi Defense Minister Khalid al-Obeidi said Iraq is balancing the assistance it receives from the U.S. and Iran. He said Tehran is primarily helping with the Shiite militias, but that Baghdad welcomes "help from any country because we are in dire need because we are at war."

NEW DETAILS ON ISIS ATTACK ON LIBYAN OIL FIELD

Militants from Libya's ISIS affiliate beheaded eight Libyan guards in an attack on a central oil field last week during which the extremists also abducted nine foreigners, a Libyan spokesman said Monday.

In the Philippines, authorities said that four Filipinos were among the nine taken captive during the assault Friday on the al-Ghani oil field, some 480 miles southeast of the Libyan capital. An Austrian, a Czech, a Bangladeshi and a Ghanaian national were also taken while one hostage remains unidentified.

A series of attacks in recent weeks have forced Libya to declare 11 oil fields non-operational, including al-Ghani, and invoke a force majeure clause that exempts the state from contractual obligations. Libya's military spokesman, Ahmed al-Mesmari, warned that Islamic State militants' long-term goal is to take over Libya's petroleum industry.

Al-Mesmari also said that during the attack, an employee watched the beheadings of the eight oil guards and subsequently died of a heart attack. He did not elaborate on how the army knew about the beheadings.