Iraq's parliament, which had been due to elect the country's president on Wednesday, postponed the vote by a day, delaying the formation of a power-sharing government urgently needed to confront a Sunni Muslim insurgency.

The advance by Sunni Islamist militants who seized swathes of northern Iraq last month has put the OPEC oil producer's survival in jeopardy. Iraqi politicians have been deadlocked over forming a new government since an election in April.

The Islamic State of Iraq and Syria, an al Qaida offshoot that is leading the insurgency, claimed responsibility for an overnight suicide bombing in a Shiite district of Baghdad that killed 33 people, one of the deadliest recent attacks in the capital.

The bloodshed highlighted the need for Iraq's politicians to form a united front against the terrorists, who want to march on the capital. The United States has made clear that it wants to see a more inclusive government established in Baghdad before providing military support against the insurgency.

Under Iraq's governing system, in place since the post-Saddam Hussein constitution was adopted in 2005, the prime minister is a member of the Shiite majority, the speaker a Sunni and the largely ceremonial president a Kurd.

Speaker Salim al-Jubouri told parliament that the Kurds had asked for a one-day delay on the vote so they could agree on a candidate. Parliament has until the end of the month to choose a president, who will then have 15 days to nominate a prime minister.

"Iraq cannot afford a protracted government formation process as the current th