In a brutal propaganda video - purporting to show the execution of a Hamas affiliate - the jihadi group declared war on the Palestinian terror group, which controls much of the Gaza Strip.
Tensions between the rival militant organisations have spiralled since 2015, when ISIS released a video saying it would overthrow Gaza's 'tyrants' for their apparent lack of religious fundamentalism.
ISIS's most recent video released on Wednesday shows the man, accused of selling weapons to Hamas, on his knees in an orange jumpsuit.
In the footage the group says it had also declared war on Hamas for its crackdown on small ultra-conservative Sunni Muslim Salafi groups in Gaza.
According to Site, a US monitoring agency that keeps track of jihadi platforms, the 22-minute video shows a man, identified as Abu Kazem al-Maqdisi, urging Islamic followers in Gaza to mount attacks on Hamas.
Maqdisi, who is originally from Gaza but now preaches hate in Sinai, says in the footage: '[Hamas] uses its smuggled weapons to empower that which was not revealed by God.
'It also fights supporters of the Islamic State in Gaza and the Sinai and prevents the migration of these supporters from Gaza to the Sinai.'
Towards the end of the recording, the narrator identifies the Hamas collaborator as Musa Abu Zamat
Zamat is then shot in the back of his head at point-blank range by an Islamist holding a pistol, reports the International Business Times.
One militant steps forward, saying: 'Never surrender to them. Use explosives, silenced pistols and sticky bombs.
'Bomb their courts and their security locations, for these are the pillars of tyranny that prop up its throne.'
The propaganda video cuts to images of Khaled Meshaal, the former Hamas leader who stepped down in April this year, alongside Iran's Supreme Leader Ayatollah Ali Khamenei.
Iran has publicly backed the Palestinian group in recent years, providing it with missiles and funding its extensive tunnel network it uses to enter Israeli territory, reports Newsweek.
Hamas has fought three wars with Israel, the last of which was in 2014.
While some thought Donald Trump's December decision to relocate the US embassy from Tel Aviv to Jerusalem would ignite a fourth war Hamas' response has been muted.
Jerusalem is contested ground and hosts holy shrines valuable to both Islam and Judaism
Both the US and the European Union have designated Hamas as an extremist organisation.
Israel's far-right often compares the group to ISIS for its radical interpretation of Islam. However, the group stops short of calling for Sharia law.
But like ISIS, the group has carried out public execution on the streets of Gaza. It claims it only does to punish those who collaborate with its nemesis Israel.