US President Barack Obama has said that Washington's offer of dialogue with Iran still stands, in his latest New Year message to the Iranian people.
He said the Iranian government had "chosen to isolate itself" but that the US still wanted justice and dignity for Iranians, and less internet censorship.
UK Foreign Secretary David Miliband said he hoped Iranians would be able to freely express their aspirations.
Correspondents say his comments will be seen as support for Iran's opposition.
'Hopeful future'
It is the second time President Obama has recorded a video message for the festival of Nowruz, a 12-day holiday celebrating the beginning of the New Year on the Persian calendar.
Last year he became the first US leader for decades to reach out directly to Iran's people and government, offering a "new beginning" in US-Iranian relations.
But since then, Mr Obama's offers of engagement over Iran's nuclear ambitions have been largely spurned, and US efforts to impose new sanctions have been slow to find wide support from UN members.
Washington has also criticised the Iranian authorities for cracking down on protestors in a series of clashes following a disputed June presidential election.
"Over the course of the last year, it is the Iranian government that has chosen to isolate itself, and to choose a self-defeating focus on the past over a commitment to build a better future," Mr Obama said.
"Even as we continue to have differences with the Iranian government, we will sustain our commitment to a more hopeful future for the Iranian people," he said.
There was a palpable change in tone from the president in this year's Nowruz message, the BBC's Madeleine Morris reports from Washington.
Whereas last year's focused on the things the Iranian and American people had in common, this year's sought more to put a positive spin on America.
Mr Obama told the Iranian people that the US was increasing opportunities for educational exchanges as well as working to increase access to internet technology so Iranians could communicate "without fear of censorship".
British message
Mr Miliband said he hoped the coming year would enable the Iranian people to fulfil their hopes and ambitions and allow them to express freely their aspirations for the future.
The Iranian government is likely to read it as a coded message of support for the opposition, or at least for the principles they say they stand for, says the BBC's Tehran correspondent, Jon Leyne, reporting from London.
As for ordinary Iranians, they know they face a year likely to be full of political and economic problems, he adds.
