Islamist insurgents seized another city, Tikrit, in Iraq today, just 24 hours after taking Iraq's third-largest city, Mosul. With Iraqi government forces more unstable than ever, the militants are rapidly advancing towards Baghdad.

The Sunni insurgents are mostly from the Islamic State of Iraq and Syria, or ISIS, which is an offshoot of Al Qaeda. In addition to overtaking Tikrit, ISIS fighters threatened a sacred shrine in Samarra today, just 70 miles north of Baghdad. Per the New York Times:

[Witnesses] said the militants demanded that forces loyal to the government leave the city or a sacred Shiite shrine there would be destroyed. Samarra is known for the shrine, the al-Askari Mosque, which was severely damaged in a 2006 bombing during the height of the American-led occupation. That event touched off sectarian mayhem between the country's Sunni Arab minority and its Shiite majority.

According to the BBC, 21 people were also killed today in a suicide bombing at a Shia meeting today in Baghdad.

Iraqi Prime Minister Nouri Maliki has vowed to fight back against the insurgents. He also said he would punish Iraqi forces who fled in the face of ISIS. Still, things don't look good: 800 people, 603 of them civilians, were killed in sectarian violence last month alone.

[Image via AP]