Acting parliament speaker Mahdi al-Hafidh said in a statement that after considering the "national interests," the next session will be on Sunday instead of Aug. 12.
He warned that any delay in forming a new government "will jeopardize Iraq's security and democracy and will increase the suffering of Iraqis." He also called on all political rivals to "shoulder their responsibilities and set aside their differences to fight terrorism to put Iraq back on the path of democracy."
Al-Hafidh's statement made official what he had said late Monday was a "preliminary agreement" among political leaders to skip the long break and move the next session up to Sunday.
Lawmakers are under pressure to quickly form a new government that can unite the country and roll back the insurgents. The legislature held its first session since April elections last week, but failed to agree on a new speaker, president and prime minister.
Despite the decision to meet Sunday instead of next month, it still appears unlikely that political leaders will be able to bridge their differences in time to settle on names for the top leadership posts - particularly the prime minister, with incumbent Nouri al-Maliki resisting a campaign to replace him.
Al-Maliki's State of Law bloc won the largest share of seats in April's election, securing 92 out of parliament's 328 seats. But he is far short of the majority needed to govern, which means he needs allies to cobble together a coalition government.
His opponents - and many former allies - want him removed, accusing him of monopolizing power during his eight years in office and contributing to the current crisis by failing to promote reconciliation with Sunnis. But he has vowed he will not abandon his bid for a third consecutive term.
The militant offensive that has plunged Iraq into its worst crisis since the last U.S. troops left in 2011 is being spearheaded by the Islamic State extremist group, which has also seized control of a huge chunk of land in neighboring Syria and essentially erased the border between the two countries.
Speaking to reporters in Washington, U.S. State Department spokeswoman Jen Psaki called the parliament's move "a positive step forward."
"We certainly welcome the announcement. But it won't stop there. It will require prompt agreement on a new parliamentary speaker and, following that, candidates for president and prime minister in order to have a successful creation or formation of a government."
On Tuesday, an airstrike targeted the mayoral building in the militant-held town of Qaim on the Iraqi side of the frontier, killing two people and wounding three others, according to Karim al-Dulaimi, a doctor at the town hospital. He said another air raid hit a few minutes later, but there was no word yet on casualties from that strike.
It was not immediately clear whether the airstrikes were carried out by the Iraqi or Syrian military. Officials say Syria has struck militant positions near the border inside Iraq at least once before.
The militant offensive has driven tens of thousands of people from their homes, many of whom have fled to the largely autonomous Kurdish region in the north.
Thousands of people, most of them ethnic Turkmens from the now militant-held town of Tal Afar, entered the self-rule Kurdish region through the Khazer crossing Tuesday. Some of them said that had been waiting for five days to get permission to enter.
"The terrorists came to us and they had weapons and everything. We couldn't face them. They were sectarian," said one woman who gave her name as Zainadeen.
Many of them said they plan on traveling to the Kurdish region's capital, Irbil, and from there by plane to the cities of Najaf and Karbala south of Baghdad.
The United Nations estimates that some 8,000 families have fled Tal Afar.