Rice left the UAE capital Abu Dhabi for Singapore, an AFP correspondent travelling with her reported.
She had flown on Monday in to Abu Dhabi where she met foreign ministers and other officials from the six Arab monarchies of the Gulf as well as Jordan, Egypt and Iraq.
Rice's warning to Tehran came after she took the unprecedented step of sending a top aide to meet Iran's chief negotiator Saeed Jalili at international talks in Geneva on Saturday.
Washington had hitherto refused to sit with Tehran on nuclear talks until Iran stopped enriching uranium.
The meeting sent a "very strong message to the Iranians that they can't go and stall… and that they have to make a decision," Rice told reporters en route to Abu Dhabi.
"It clarifies Iran's choices and we will see what Iran does in two weeks."
Rice briefed Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed al-Nahayan on the Geneva talks and discussions on the Iranian nuclear file, the UAE's offical WAM news agency reported.
Rice said the discussions with Gulf and other Arab officials would cover the Middle East peace process, Lebanon, Syria, Iran, Iraq and Afghanistan.
WAM said Abu Dhabi's crown prince, whose country has strong economic links with Iran despite a territorial row, called for "diplomatic solutions" to regional problems — a position in line with repeated calls by Arab states in the Gulf for a negotiated settlement to the Iranian nuclear standoff.
Rice headed to Singapore for meetings with the Association of Southeast Asian Nations — highlighted by talks on North Korea's nuclear programme — and was due to travel on to Australia, New Zealand, Samoa and Hawaii.
