US President Barack Obama on Tuesday accused Iran's leaders of imposing an "electronic curtain" of censorship, announcing steps to use software and social media to help Iranians gain freer access to the Internet.
Obama also directly told Iranians in a message for Nowruz, the Iranian New Year, that if their government took a "responsible path" on its nuclear program the country could enjoy the benefits of exiting isolation.
But Iran's supreme leader Ayatollah Ali Khamenei, firing his own shot in the propaganda war, warned that Tehran would hit back hard at any US or Israeli attacks, and again denied seeking nuclear weapons.
Obama said in his YouTube message carried in English, Persian and Arabic, coming at a time of rising tensions between Washington and Tehran, that there was "no reason" for Americans and Iranians to be divided.
"An electronic curtain has fallen around Iran -- a barrier that stops the free flow of information and ideas into the country, and denies the rest of the world the benefit of interacting with the Iranian people," Obama said.
Obama accused Iran of curtailing Internet freedoms, jamming foreign television and radio broadcasts, monitoring computers and cellphones, and cracking down on freedom of expression on the Internet.
"In recent weeks, Internet restrictions have become so severe that Iranians cannot communicate freely with their loved ones within Iran, or beyond its borders," he said.
"Technologies that should empower citizens are being used to repress them."
His use of the phrase "electronic curtain" recalled former British prime minister Winston Churchill's speech in Missouri in 1946 in which he warned that a Soviet "iron curtain" had fallen across post-war Europe.
Obama announced new measures to make it easier for US software companies to market chat and social network programs in Iran, including Skype, Yahoo Messenger, Google Talk and browsers like Firefox and Internet Explorer.
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Plug-ins like Flashplayer, Shockwave and Java would also be included as long along with other personal data storage systems like Dropbox.
Obama also highlighted the Virtual US Embassy project, which reaches out to Iranians using Farsi, Facebook, Twitter and Google Plus.
In Iran, Khamenei said amid a flurry of speculation that Israel may launch a preemptive strike against Iranian nuclear facilities, that the Koran stated that if an enemy attacks, it will be defeated.
"We have said that we do not have atomic weapons and we will not build any," the religious leader said.
"But if there is any attack by the enemies, whether it be United States or the Zionist regime, we will attack them at the same level as they attack us," he said in live televised Nowruz speech.
Millions of Iranians -- along with people of other Persian-influenced nations such as Afghanistan -- celebrate Nowruz with the start of spring, which is meant to represent renewal.
Iran and the United States have no diplomatic relations. Washington has repeatedly urged Iran's clerical regime to improve its record on human rights, including treatment of political critics and religious minorities.
The Obama administration has since ramped up economic sanctions to pressure Iran to end its nuclear program, as Israel leads calls for the world to ensure that Tehran does not develop an atomic bomb.
The New York Times reported on Tuesday that a classified US war simulation had predicted that an Israeli attack on Iran would spark a regional war and "dire consequences" that would embroil the United States.
The latest rhetorical exchanges between Washington and Tehran precede expected talks agreed to by Iran and the P5+1 group of powers -- the five permanent UN Security Council members plus Germany.
Iran has formally requested a date and venue for the negotiations, the previous round of which collapsed in Istanbul in January last year.