The three-day tour will include Hillary Clinton's first trip to Saudi Arabia
US Secretary of State Hillary Clinton has warned Iran that the West will impose "greater costs for its provocative steps".
She spoke at the US-Islamic World forum in Qatar during a trip to rally Arab support for tougher sanctions against Iran over its nuclear programme.
She said the West was "encouraging Iran to reconsider its dangerous policy decisions."
The three-day Gulf tour will include her first trip to Saudi Arabia.
Mrs Clinton is due to meet Turkish premier Recep Tayyip Erdogan, whose country opposes the sanctions.
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.
Hillary Clinton begins her tour to Middle East today
The U.S. Secretary of State Hillary Clinton, begins her tour today of the Middle East, which includes Qatar and Saudi Arabia, in an effort by the U.S. administration to exert more diplomatic pressure on Iran though the Arab countries, where the tour is for three days, as today Clinton is meeting with Prime Minister of Qatar Sheikh Hamad bin Jassim Al-Thani while tomorrow, she will meet the Saudi king Abdullah bin Abdul Aziz.
In regards to Palestine-Israel conflict, it is expected to discuss with Clinton officials in Qatar and Saudi Arabia, ways to restart peace talks between the two sides, as peace talks between the two countries have been frozen for more than a year.