Prince Charles has arrived in the Iranian city of Bam, which was devastated by an earthquake last year.
Charles was welcomed at Iran's foreign ministry
The trip marks the first visit to Iran by a British royal since the Queen Mother visited in 1975.
The Prince of Wales met President Mohammad Khatami in Tehran before travelling south to Bam.
On Sunday he made a surprise morale-boosting visit to British troops stationed in Basra, Iraq, where he praised their "remarkable example".
The prince later flew from Iraq to Tehran's Mehrabad airport, where he was met by
British Ambassador Richard Dalton.
At a reception at St James's Palace on Friday, Charles called for renewed international efforts to rebuild the city of Bam, where 40,000 people lost their lives on 26 December.
Andrew Dunn, of the British Embassy in Tehran, said: "Prince Charles is patron of the British Red Cross and he is coming in that role."
"It's a completely non-political visit."
Mostapha Mohaghegh, director of International Affairs at the Iranian Red Crescent, who will meet the prince, said 200,000 people would need help in the earthquake's aftermath in the months and years to come.
He told BBC Radio 4's Today programme the Royal visit was a "unique opportunity" for the Prince to see how the relief operation was working.
"This will be very useful and will have a positive effect," he said.
Relations between Iran and Britain have warmed in recent years
and the prince's visit comes amid celebrations marking the 25th
anniversary of the creation of the Islamic republic.
Earlier on Sunday, the prince became the first member of the Royal Family to visit Iraq since the recent conflict.
Charles landed at Basra International Airport from Kuwait, in a C130 Hercules armed with equipment to deflect any surface-to-air missiles.
He flew by Chinook to the Al-Sarraji Palace compound, accompanied by a helicopter gunship firing flares.
Before he touched down gunfire was heard over the city.
But Charles shed his armoured body vest as he prepared to meet troops working to restore peace and stability in Iraq's second city in the aftermath of the war.
About 9,000 British soldiers are serving in Iraq with 4,500 based in Basra.
A spokesman for Charles said: "We don't normally take the prince to places as dangerous as this. The troops need cheering up."
Among the servicemen and women Charles met were members of the Royal Regiment of Wales, the 2nd Battalion of the Parachute Regiment and the Army Air Corps.
He thanked British troops for their work in Iraq, saying: "You are a remarkable bunch of people and I can only salute you.
"You have a great way of conducting that all-important hearts and minds campaign."
Charles added the troops were owed a great debt of gratitude.
The prince also met Paul Bremer, the US's top administrator in Iraq, who said: "This is a very important demonstration of the British Government's commitment to what we have started here."