Iraqi forces try to seal off Islamic State around Tikrit

Iraqi security forces and Shi'ite fighters reload a weapon during clashes with Islamic State militants in Salahuddin province March 2, 2015. REUTERS/Thaier Al-Sudani

BAGHDAD (Reuters) - Thousands of Iraqi soldiers and Shi'ite militiamen sought to seal off Islamic State fighters in Tikrit and nearby towns on Tuesday, the second day of Iraq's biggest offensive yet against a stronghold of the Sunni militants.

Iranian military commander Qassem Soleimani, who has helped coordinate Baghdad's counter-attacks against Islamic State since it seized much of northern Iraq in June, was overseeing at least part of the operation, witnesses told Reuters.