BEIRUT (Reuters) - A Hezbollah commander has died during a mission in Iraq, sources familiar with the incident said on Wednesday, indicating the Lebanese group that is already fighting in Syria's civil war may be involved in a second conflict in the region.

Hezbollah, an Iranian-backed Shi'ite Islamist group, has not previously announced any role in the conflict in Iraq, which escalated last month when radical Sunni militants seized large areas of territory from the Shi'ite-led government in Baghdad.

Four sources in Lebanon named the Hezbollah commander as Ibrahim al-Haj, a technical specialist involved in training. They said he was "martyred" in a battle near Mosul, a city in northern Iraq seized from government control last month by an al Qaeda offshoot known as the Islamic State.

His funeral was held on Wednesday in the village of Qilya in the Bekaa Valley. A Hezbollah official contacted by Reuters declined to comment.

Hezbollah's deployment in Syria has helped President Bashar al-Assad's government firm up its grip on power by reestablishing control over a strategic corridor of territory stretching north from Damascus. The group says it is fighting in Syria against the threat posed by radical Sunni militants.

Assad is an ally of Iran and a member of the Alawite sect that is an offshoot of Shi'ite Islam. Tehran also has longstanding ties to Shi'ite politicians in Iraq.

Hezbollah was founded with Iranian help in the early 1980s and fought to drive out Israeli forces that occupied southern Lebanon until 2000. The most powerful group in Lebanon, it also fought a war with Israel in 2006.

(Reporting by Laila Bassam; Writing by Tom Perry, Editing by Angus MacSwan)