Islamic State terrorists conquered large areas of the Yarmouk Palestinian refugee camp in the Syrian capital Wednesday and are battling Palestinian faction Aknaf Beit al-Maqdis for control, media reports indicate.

"Fighters from ISIS launched an assault this morning on Yarmouk and they took over the majority of the camp," said Anwar Abdel Hadi, Damascus-based director of political affairs for the Palestine Liberation Organization (PLO).

This latest incursion represents ISIS' most significant territorial gain into Syria's capital.

Meanwhile, a senior Hamas leader Yehia Hourani, was killed in the camp on Monday, according to a Hamas statement which referred to Hourani's death as an assassination.

Yarmouk once hosted 160,000 Palestinians and Syrians. Now, however, only about 18,000 people remain in the camp that has been controlled by various groups over the past four years. Originally under dictator Bashar al-Assad's rule, the Yarmouk camp was taken over by moderate Sunni rebels and at one point also conquered by the al-Qaida affiliate Jabhat al-Nusra.

The siege has caused significant food and water shortages, imposing a humanitarian crisis over the camp's remaining inhabitants.