Prince Charles has seen at first hand the devastation caused in the earthquake-hit city of Bam in Iran.
The visit was the first by a British royal in decades
Charles toured the city, meeting survivors of the earthquake that killed an estimated 42,000 people and injured more than 30,000 on 26 December.
He was the first British royal to visit Iran since the 1970s.
The Prince of Wales has now flown to Riyadh in Saudi Arabia, but earlier gave his condolences to the Iranian President Mohammad Khatami in Tehran.
Their meeting was "warm and cordial", according to one of his aides.
The visit came amid celebrations marking the 25th
anniversary of the creation of the Islamic republic in 1979.
The two men discussed the prince's visit the previous day to neighbouring Iraq.
The president spoke of "the need for a free election [in Iraq] under UN supervision".
But Clarence House insisted the purpose of Charles' trip was humanitarian.
Andrew Dunn, of the British Embassy in Tehran, said before the visit: "Prince Charles is patron of the British Red Cross and he is coming in that role."
"It's a completely non-political visit."
Arriving in Bam, Charles toured the rubbish-lined streets, watched by local people from the tents where they have lived since the earthquake demolished their homes.
He said: "My people in Britain are very concerned and they're praying for the Iranian
Charles also visited a date orchard and met farmers trying to rebuild the ancient underground irrigation structures, the Qanat.
His visit to Saudi Arabia comes as relations with the UK are starting to improve.
They had gone through a rocky period after a number of Britons were imprisoned over allegations of making explosions, and the kingdom was criticised for its lack of action over Islamist militants.
Charles knows the Saudi ruling family well and is considered ideal for the role of helping to build on warming relations.
Iranian Red Crescent International Affairs director Mostapha Mohaghegh said 200,000 people would need help in the earthquake's aftermath in the years to come.
During the earlier visit to Iraq on Sunday - the first by a British royal since the nation was created in 1919
- Prince Charles met troops working to restore stability in the aftermath of the war.
He also met Paul Bremer, the US top administrator in Iraq.