BAGHDAD — Al-Qaida-inspired militants today seized effective control of Saddam Hussein’s hometown of Tikrit, expanding their offensive closer to the Iraqi capital as soldiers and security forces abandoned their posts following clashes with the insurgents.

Fighters from the Islamic State of Iraq and the Levant took control a day earlier of much of Mosul, Iraq’s second-largest city, in a major blow to the authority of the country’s Shiite government. An estimated half a million residents fled the economically important city.

Residents reached by telephone in Sunni-dominated Tikrit said the Sunni militant group had taken over several police stations.

Two Iraqi security officials confirmed Tikrit was under the control of the ISIL, and said the provincial governor was missing. Tikrit, the capital of Salahuddin province, is 80 miles north of Baghdad.

Prime Minister Nouri al-Maliki said the massive security failure in Sunni-dominated Nineveh Province that allowed militants to seize Mosul was the result of a “conspiracy,” and that those members of the security forces who fled rather than stand up to the militants should be punished.