The US president has reiterated his administration's offer of dialogue with Iran, but said that Tehran's leaders had "turned their backs" on previous overtures. 

In a video broadcast on the internet on Saturday, Barack Obama also pledges to ensure that Iranians can get better access to the web without censorship.

"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," Obama said in the video.

He told Iranians that "our offer of comprehensive diplomatic contacts and dialogue stands".

"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."

The video, which carried subtitles in Farsi, was timed to coincide with Nowruz, a 12-day festival celebrating the Persian new year and the arrival of spring.

It was posted a year after he offered a new beginningfor relations in a similar video.

Internet censorship

In the latest video, Obama offered increased educational programmes to allow young Iranians to study in the US, and suggested that Washington would take an active role to ensure online communication.

He promised US efforts to "ensure that Iranians can have access to the software and internet technology that will enable them to communicate with each other, and with the world, without fear of censorship".

Opposition supporters in Iran used social networking sites and services such as Twitter, Facebook and the Google-owned YouTube website to get their message out following the country's disputed presidential election.

During protests last June, the US state department took the unusual step of asking Twitter to delay planned maintenance because of its use by Iranian opposition supporters.

Some Iranian news websites carried reports about the message, but did not post the video itself or go into detail about what Obama said.

'Iranophobic' message

State radio said in a commentary that Obama's video was intended to create a rift among Iranians.

"They are pursuing the same Iranophobic policy, opposing the scientific achievements of Iran in the nuclear and space fields and portraying them as military programmes to manipulate international public opinion," it said.

Obama's address comes against a backdrop of efforts to impose international sanctions on Iran over its nuclear programme, which the West says could be used to build nuclear weapons.

Tehran rejects that, saying its nuclear programme is for purely civilian purposes.

International support for the sanctions has been slow and Obama has in the past signalled a willingness to engage Iran in dialogue.

At his inauguration last year, Obama said his administration would reach out
to rival states, declaring "we will extend a hand if you are willing to unclench your fist".