The United States is to temporarily ease sanctions on Iran to help relief supplies following the Bam earthquake.
The Americans are the first to set foot officially in Iran for 24 years
The move - in force for 90 days - will make it easier for American citizens and agencies to transfer money to Iran.
A White House spokesman said the move was to meet "extraordinary humanitarian needs" following the devastating quake which left 50,000 dead.
Another 100,000 people were left homeless and most have now been housed in tents, according to a UN aid team.
"The Iranian people deserve and need the assistance of the international community to help them recover from the catastrophic results of last week's earthquake," said US spokesman Trent Duffy in a statement.
"The American people want to help, and share great concern and sympathy for those families and individuals who lost loved ones, their homes and possessions."
Currently, it is against US law to transfer any money to Iran, so even disaster relief payments have to be authorised by the US Treasury.
He said the US Treasury would issue a general licence temporarily enabling US citizens and non-governmental organisations (NGOs) to support aid activities in and around Bam.
It is not clear if the latest US announcement was intended as anything more than a practical measure to help the relief effort, says the BBC's State Department correspondent, Jon Leyne.
US Secretary of State Colin Powell had hinted, during an interview with the Washington Post on Tuesday, at a possible warming of relations with Iran.
But Trent Duffy told reporters: "We've made clear to the Iranian government on many occasions our grave concerns regarding its support for terrorism, pursuit of weapons of mass destruction and other of its activities."
Aid workers from the US have already joined the effort to help survivors, in the first official representation by Americans since Washington cut ties with Iran after the 1979 revolution.
An 80-strong US team has started setting up a field hospital - the first to operate since Bam's own two hospitals were flattened in the earthquake.
USAid spokesman Dewy Perks told the BBC it was an honour to be helping the people of Iran on behalf of the US Government. It was "not about politics, it's about humanitarian relief," he said.
Iranian President Mohammed Khatami welcomed US participation in the aid effort.
But he has stressed that it did not change relations between the two countries who severed ties following the Islamic Revolution of 1979.
"We must not turn down humanitarian assistance... to help human beings who have suffered injury and we do not turn it down but this has nothing to do with the political problems between us," he said on Iranian radio.
Aid agencies say disaster victims need at least:
Shelter: 3.5 square metres
Water: 7 litres/day
Food: 2,100 kilocalories/day
The US announcement came as four aftershocks shook the ancient Silk Road city of Bam on Wednesday, in the wake of last Friday's quake.
Teams from 40 countries are at work in and around the city where most of the survivors remain close to their homes, some 90% of which were destroyed in the disaster.
UN aid workers say most of the 100,000 people left homeless are being housed in tents; water supply has been restored and a steady stream of humanitarian aid is flowing into the city.
However, correspondents say many people are still without shelter, and face yet another night of cold and hunger.