"There can be no explanation for this delay," said Ammar Toma, a Shiite MP from the Fadhilah party. "There are important matters on the table: the fate of the displaced, the security situation."
US President Barack Obama, UN chief Ban Ki-moon and visiting French Foreign Minister Laurent Fabius have, over the past two days alone, stressed that Iraq needed a new and united government to lead the fight against jihadists who control large parts of the country.
Many blame the crisis on Prime Minister Nuri al-Maliki, whose policies critics say marginalised Sunni Arabs, pushing them into the arms of jihadists.
Despite winning April polls comfortably, the deadly two-month-old conflict has made his position untenable.
Maliki has lost the support of many former allies, including Washington, Tehran, Iraq's influential Shiite religious leadership and a significant part of his own Dawa party.
But the 64-year-old has dug his heels in and Iraq's fractious parliament has so far been unable to agree on an alternative.