This file image posted on a militant website on Jan. 7, 2014, which is consistent with AP reporting, shows a convoy of vehicles and fighters from the Al-Qaeda splinter group Islamic State of Iraq and the Levant (ISIL) fighters in Iraq’s Anbar Province.

WASHINGTON: Militants who have seized a large swathe of northern and north-central Iraq now plan to march on the capital Baghdad, a US-based monitoring group said Wednesday.

In a lightning offensive, Islamic State of Iraq and the Levant militants seized Tikrit earlier, its latest success following a spectacular assault late Monday on Mosul, a city of two million.

The militants’ advances have forced as many as half a million people to flee their homes.

ISIL spokesman Abu Mohammed Al-Adnani promised that the battle would “rage” on Baghdad and Karbala, a city southwest of the capital that is considered one of the holiest sites for Shiite Muslims, the SITE Intelligence Group said.

“Do not relent against your enemy… The battle is not yet raging, but it will rage in Baghdad and Karbala,” Adnani said, according to a SITE translation of an audio statement released on the militants’ Twitter feed.

“Put on your belts and get ready.”

Adnani also dismissed President Nuri Al-Maliki as woefully incompetent, calling him an “underwear salesman.”

“What have you done to your people, O foolish one. No one is more foolish than you but those who accept you as the president and commander,” Adnani said in the translated statement.

“What do you know about policy, leadership, and military command? You lost a historic opportunity for your people to control Iraq, and the Shiites will always curse you for as long as they live. Indeed, there is between us and you a balance to be made even.”

ISIL was originally Al-Qaeda’s branch in Iraq, but it used Syria’s civil war to vault into something more powerful. It defied orders from Al-Qaeda’s central command and expanded its operations into Syria, ostensibly to fight to topple Assad. But it has turned mainly to conquering territory for itself, often battling other rebels who stand in the way.

Tikrit — hometown of executed dictator Saddam Hussein — was the second provincial capital to fall in as many days as the jihadists and their allies captured a string of mainly Sunni Arab towns where resentment against the Shiite-led government runs deep.

After Tikrit’s fall, the operation spread down the main highway toward Baghdad, with militants battling security forces on the northern outskirts of Samarra, just 70 miles (110 kilometers) from the capital.

State television said security forces responded with air strikes, and residents said the fighting subsided without the militants entering the city.

Samarra is mainly Sunni Arab but is home to a shrine revered by the country’s Shiite majority, whose bombing by Al-Qaeda in 2006 sparked a Shiite-Sunni sectarian conflict that left tens of thousands dead.