Vice President Eshaq Jahangiri made the pledge during talks in Tehran with his Iraqi counterpart, former premier Nuri al-Maliki.
"In the face of terrorism, we must use all means... Iran is ready to place all of its abilities at Iraq's disposal," Jahangiri said, the website of Iranian state broadcaster IRIB reported.
To help counter a lightning IS offensive launched on June 9, Iran has supplied Iraqi Kurds with weapons and sent military advisers to Baghdad, while also denying it had deployed ground troops.
However, early last month Iranian television published a rare picture of its elite Quds Force chief, Major General Qassem Suleimani, on an Iraqi battlefield alongside Kurdish peshmerga forces.
And in September, a senior Iranian military official threatened to attack deep inside Iraq if the jihadists approached Iraq's border with the Islamic republic.
Tehran, which has refused to join the international coalition against IS, advocates regional support for the Iraqi and Syrian governments, and says that air strikes are insufficient.
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Jahangiri on Monday dismissed the coalition strikes as a "show" and criticised the US-led campaign for not taking "concrete measures to dry up financial supplies" to the jihadists.
Maliki, meanwhile, said "wider cooperation and coordination are needed to prevent greater dangers" that lie ahead.
Iraq's ex-prime minister, who stepped down in August in favour of Haidar al-Abadi following a protracted political crisis, also met Iran's supreme leader.
Ayatollah Ali Khamenei praised Maliki's "courage" during eight years in power, and said his decision to step aside helped to prevent instability in Iraq.
In October, Abadi also visited Tehran to discuss Iraq's battle against the IS offensive.
The mainly Shiite neighbours have been close since the ouster of Sunni dictator Saddam Hussein in the US-led invasion of 2003, with Tehran's role becoming increasingly open in recent years.