LONDON (Reuters) - U.S. Secretary of State John Kerry said on Friday he expects President Barack Obama to decide quickly on what steps the U.S. will take to help combat the relentless advance of the Islamist insurgency in Iraq.

"Given the gravity of the situation, I would anticipate timely decisions from the president regarding the challenge," Kerry told reporters at a news conference with British Foreign Secretary William Hague.

"I am confident the US will move rapidly and effectively to join with our allies in dealing with this challenge," Kerry added.

Obama said on Thursday he was considering "all options" to support Iraq's Shi'ite Muslim-dominated central government that took full control when the U.S. occupation ended in 2011, eight years after the 2003 invasion that toppled Saddam Hussein.

Kerry also said Iraqi Prime Minister Nuri al-Maliki should do more to put sectarian differences aside in his country.

"Prime Minister Maliki and all Iraqi leaders need to do more to put sectarian differences aside," Kerry said, alluding to long-standing Western complaints that the Shi'ite Prime Minister has done little to heal sectarian rifts that have left many of Iraq's minority Sunnis, cut out of power since Saddam's demise, aggrieved and keen for revenge.

(Reporting By Arshad Mohammed; editing by Stephen Addison)