US Secretary of State Hillary Clinton is to arrive in the Gulf to rally Arab support for tougher sanctions against Iran over its nuclear programme, BBC reported.
In Qatar, Mrs Clinton will address the annual US-Islamic World Forum and meet Turkish premier Recep Tayyip Erdogan, whose country opposes the sanctions.
The three-day tour will include her first ever trip to Saudi Arabia.
The Obama administration is stepping up pressure on Iran by launching a diplomatic offensive in the Gulf.
Washington wants the UN Security Council to impose a fourth round of sanctions on Tehran.
Iran says its nuclear programme is to generate electricity so it can export more of its valuable oil and gas, but the West suspects it of trying to develop atomic weapons.
Efforts to revive the Arab-Israeli peace process are also expected to be on the agenda during Mrs Clinton's tour.
The secretary of state delayed her trip by one day after her husband, former President Bill Clinton, underwent a heart procedure at a New York hospital.
In Qatar, she will hold talks with Prime Minister Sheikh Hamad bin Jasim al-Thani.
And in Saudi Arabia, Mrs Clinton will meet King Abdullah, as well as foreign minister Prince Saud al-Faisal.
A state department official travelling with Mrs Clinton said the US expected Saudi Arabia, which has growing trade relations with China, to persuade Beijing to abandon opposition to tougher sanctions against Iran.
"We would expect them [the Saudis] to use these visits, to use their relationships in ways that can help increase the pressure that Iran would feel," Jeffrey Feltman, assistant secretary of state, told reporters as Mrs Clinton began her trip.
Loss of revenue
China, which wields a veto on the UN Security Council, is still opposed to a fourth round of sanctions.
The BBC's Kim Ghattas, who is travelling with Mrs Clinton, says Beijing fears major loss of revenue from investments in Iran and disruption in oil supplies from the country.
The secretary of state is expected to press the Saudis to reassure the Chinese that the kingdom can offset any disruption.
Missile defence is also expected to be on the agenda - the US is beefing up the missile deterrent of its Arab allies to assure them that their security is key to Washington.
Mrs Clinton's two deputies will head to the region in the coming days, travelling to Israel, Jordan and Egypt.
And on Monday, William Burns, the under-secretary for political affairs, will travel to Lebanon and Syria.
Our correspondent says Washington is still hoping it can loosen the links between Damascus and Tehran.
She adds Lebanon currently holds a seat on the Security Council and its ties with Iran may prevent it from backing new sanctions.
The centrepiece of Mrs Clinton's trip is a speech on Sunday at the US-Islamic World Forum, a meeting hosted by the Qatari government and the Washington-based Brookings Institution think tank.
Aides described her appearance as a sequel to US President Barack Obama's speech last June in Cairo, in which he called for an end to the "cycle of mistrust and discord" between the US and the Muslim world.