The Islamic State (IS) militant group is the single greatest threat facing the people of Iraq and the world cannot watch its spread of "evil", US Secretary of State John Kerry says.
Mr Kerry, on a Middle East tour, told a news conference in Iraq there would be a global plan to defeat IS, but the new Iraq government must be the "engine" of that fight.
IS has seized large areas of northern Iraq, overrunning the army and gaining backing from some disaffected Sunnis.
Mr Kerry made an unannounced visit to the Iraqi capital Baghdad at the start of a tour of Middle Eastern capitals aimed at boosting military, political and financial support for the fight against IS, the BBC reports.
US President Barack Obama is due to give details later of the US strategy to tackle IS.
The US Secretary of State held talks with Iraq's new Prime Minister Haidar al-Abadi, who appealed for international support to defeat the "cancer" of IS.
"Of course, our role is to defend our country, but the international community is responsible to protect Iraq," Mr Abadi said after meeting Mr Kerry.
The two men also discussed Mr Abadi's plans for his new government.
The prime minister, a Shia, has promised to devolve more power to Sunnis and tackle the central government's relations with the Kurdish minority. He has also said he will overhaul the military and make it more inclusive.
The US Secretary of State said he was very encouraged by Mr Abadi's commitment to reform. "A new and inclusive Iraqi government has to be the engine of global fight against (Islamic State)," Mr Kerry said.
The previous Shia-led government of Nouri Maliki was accused of exacerbating sectarian tension by excluding Sunnis from power and failing to deal with Kurdish demands.