Iran's nuclear deal with world powers is a sign of a common will to end conflict in the region and defeat the Islamic State jihadist group, Iraq's premier said Wednesday.

"Daesh seeks to drag our region into perpetual conflict," Haider al-Abadi said on social media, using an Arabic acronym for IS.

"The Iran deal expresses a common will to bring peace and security to our region," the prime minister said.

IS controls large parts of Iraq and Syria and has, over the past year, spread to other countries such as Egypt and Libya, where its franchises are also wreaking havoc.

Iran and major powers, led by the US, sealed a historic deal Tuesday in Vienna aimed at ensuring Tehran does not obtain the nuclear bomb, easing the Islamic republic's international isolation.

The accord aims to resolve a 13-year standoff over Iran's nuclear ambitions after repeated diplomatic failures and threats of military action.

In Iraq, Washington and Tehran have been competing to be Baghdad's top partner in the battle to regain the ground lost to the jihadists last year.

The United States, which occupied Iraq for more than eight years after removing former president Saddam Hussein in 2003, is leading an international coalition that carries out daily air strikes.

It also has thousands of trainers and advisers on the ground, helping the Iraqi military rebuild after the June 2014 debacle that saw IS capture Iraq's second city Mosul and almost a third of the country.

Iran likewise has advisers in Iraq but mostly supports Shiite militia groups, which have played a leading role in the fightback.

Baghdad's top foreign partners in the protracted military effort to reconquer jihadist-held land have been keen to avoid being seen as working together.

Iran has accused Washington of being responsible for the rise of IS -- considered the most powerful and brutal group in modern jihad.

Some Shiite militia groups have carried out deadly attacks against US troops in the past and Washington sees the soaring influence of paramilitary organisations with a dubious rights record as a concern for the future.