BAGHDAD (Reuters) - An Iraqi Shi'ite militia group said on Friday it would attack U.S. interests in Iraq and the region if Washington carries out a military strike on Syria.

President Barack Obama said on Friday the United States was still in the planning process for a response to the chemical weapons use in Syria.

"All their interests and facilities in Iraq and the region will be targeted by our militants if the United States insists on attacking Syria," a spokesman for the Iraqi militia group al-Nujaba'a told Reuters by telephone, without giving details.

Al-Nujaba'a is an umbrella group which includes Iraqi Shi'ite militants who have crossed into neighbouring Syria to fight alongside troops loyal to Syrian President Bashar al-Assad. Assad is from the Alawite sect, an offshoot of Shi'ite Islam.

The group includes fighters of the Asaib al-Haq and Kata'ib Hezbollah militias and the Mehdi army militia of anti-U.S. Shi'ite cleric Muqtada al-Sadr, which was mostly disbanded after its defeat by Iraqi and U.S. forces in 2008.

Syria's war has been a delicate foreign policy problem for Iraq's Shi'ite leadership. Baghdad is close to Iran, Syrian President Bashar al-Assad's ally, but insists it takes no sides as the Syrian conflict widens a regional Shi'ite-Sunni divide.

Shi'ite militants threatened to strike U.S. interests in Iraq in September last year over a film about the Prophet Mohammad that triggered protests in Libya, Egypt and Yemen.

(Reporting by Suadad al-Salhy; editing by Andrew Roche)