US Secretary of State John Kerry and Saudi King Abdullah briefly discussed global oil supplies during a meeting on the crisis in Iraq on Friday, a senior State Department official said.

During the talks, Kerry referred to recent comments by a Saudi oil official that the world's largest oil producer would increase supplies should crises in Iraq or Syria disrupt supplies, the official said.

"The secretary noted positively a recent statement from an oil official in the kingdom reflecting the kingdom's desire to do what will be required in the event of any turbulence," said the State Department official, who briefed reporters on the talks.

The official said Kerry believed the Saudi official's comments were "constructive."

US officials have expressed the belief that concerns in oil markets will ease once a more inclusive government is formed in Baghdad that can deal with a Sunni insurgency threatening to break apart Iraq.

Saudi was Kerry's last stop in a week-long tour of capitals in Europe and the Middle East, which included a visit to Baghdad, to address the crisis that threatens to tear apart Iraq.

The US wants the Saudi Arabia to use its influence among fellow Sunnis in Iraq to press them to join the new government.

 Kerry met Syrian rebel leader Ahmad Jarba at Jeddah airport and told him that the moderate opposition he heads would be important in repelling ISIL, the al Qaeda offshoot which is fighting in both Syria and Iraq.

Kerry on Friday visited the Middle East to press regional leaders to tackle the threat from Islamist militants in both conflicts - a task given greater urgency by the situation in Iraq, where ISIL, the Islamic State in Iraq and the Levant, has captured a series of towns and cities.

"We have even more to talk about in terms of the moderate opposition in Syria, which has the ability to be a very important player in pushing back against ISIL's presence," Kerry told Jarba in the meeting at the start of his brief Saudi trip.

"President Jarba represents a tribe that reaches right into Iraq. He knows people there, and his point of view and that of the Syrian opposition will be very important going forward," said Kerry before a scheduled meeting with Saudi King Abdullah.

The Obama administration on Thursday asked for $500 million from Congress to train and equip vetted members of Syria's opposition, the most significant US move so far to support those fighting against President Bashar al-Assad.

Saudi Arabia has been the most prominent backer of the Syrian rebels, and was very critical of Washington last year when it backed away from air strikes against Assad after a poison gas attack in Damascus.

Jarba told Kerry that the worsening situation meant more effort would be needed by both Washington and Riyadh, as well as others, to address the situation in Iraq, whose border with Syria he said was now "practically open".

"The policies of Iraqi Prime Minister Nuri al-Maliki after eight years in power have resulted in greater division. Now the situation is very grave," he said.

Saudi Arabia has long distrusted Maliki as being too close to Iran and sees him as ruling on behalf of Iraqi Shi'ites to the exclusion of Sunnis. Last week Saudi officials, in an apparent message to Tehran, warned that foreign countries should stay out of Iraq.

Baghdad is racing against time as the insurgents consolidate their grip on predominantly Sunni provinces, and Kerry has been pushing Saudi Arabia to use its influence among fellow Sunnis in Iraq to join the government and ensure it represents everyone.

Kerry met the monarch at his palace in Jeddah, where the US delegation was ushered into the large marble-columned lobby of the palace. The king, who is over 90, spoke clearly in Arabic but did not get up when Kerry entered the large room.

On Thursday, Kerry met with foreign ministers from Saudi Arabia, Jordan and UAE to inform them of plans for air strikes against ISIL once a new government is formed.

The United States also wants these countries to do more to cut off the flow of funding from private donors to ISIL.-Reuters