Iraq's embattled Prime Minister Nouri al-Maliki, in a surprise speech late Sunday, resisted calls for his resignation and accused the country's new president of violating the constitution, plunging the government into a political crisis at a time it is battling advances by Islamic State fighters.

Maliki is seeking a third-term as prime minister, but the latest crisis has prompted even his closest allies to call for his resignation. A parliament session scheduled for Monday to discuss the election and who might lead the next Iraqi government was postponed until Aug. 19.

On Sunday night, in a nationally televised speech, Maliki declared he will file a legal complaint against the new president, the veteran Kurdish politician Fouad Massoum, for committing "a clear constitutional violation."

Maliki, whose Shiite-dominated bloc won the most seats in April elections, accused Massoum of neglecting to name a prime minister from the country's largest parliamentary faction by Sunday's deadline. He said the president has violated the constitution "for the sake of political goals."

Maliki, speaking on Iraqi TV for the first time since U.S. forces launched airstrikes and humanitarian airdrops in Iraq last week, said the security situation would only worsen as a result of Massoum's actions.

The political infighting could hamper efforts to stem advances by Islamic State fighters who have seized a large swath of northern and western Iraq in recent weeks.

A bloc comprising Iraq's biggest Shi'ite parties is close to nominating a prime minister, the deputy speaker of parliament said on Monday, directly challenging Maliki who has refused to give up his bid for a third term.

Abadi is one of the people mentioned as a possible successor to Maliki. In his tweet Abadi said government forces were moving around the capital in anticipation of security breaches.

Soon after Maliki’s speech, the State Department spokeswoman Jen Psaki said the U.S. rejects any effort to use coercion or manipulation in the process of choosing a new Iraqi leader. She said the U.S. supports the process to select a prime minister "by building a national consensus and governing in an inclusive manner."

Although there were rumors Sunday night of Maliki deploying special forces in Baghdad, a U.S. official speaking on condition of anonymity, said he had spoken to Massoum and his aides, who said reports of tanks surrounding the presidential compound were not true.

Having tanks stationed at the entrance to Baghdad's Green Zone, which houses government buildings, was common, the official said.

Wire services