It was the first closure of a newspaper since President Mahmoud Ahmadinejad came to office last year - and the heavy response, along with public apologies by Iranian officials, suggested the government worries the U.S. may try to stir up trouble among Iran's ethnic minorities.
Iranian officials quickly stressed the nation's unity in the standoff with Washington, which accuses Iran of seeking to develop nuclear weapons.
"It is clear that the evil hands of foreigners are making efforts to provoke tribal, ethnic, and religious differences under the present circumstances," State Public Prosecutor Ghorban Ali Dorri Najafabadi was quoted Tuesday as saying by state-media.
Hundreds of Azeris marched Monday in the northwestern city of Tabriz, protesting the cartoon. Some broke windows of the governor's office, and police had to use tear gas to disperse the demonstrators, witnesses said. The violence was also reported in an independent news agency, ILNA.
Azeris, a Turkic ethnic group, are Iran's largest minority, making up about a quarter of Iran's 70 million people, dominated by ethnic Persians. Azeris speak a Turkic language shared by their brethren in neighboring Azerbaijan, the AP reports.
Culture Minister Saffar Harrandi appeared on state television Monday night and apologized for the cartoon.
But Azeri legislator Eshrat Shayegh said the apology came "at least one week" too late.
Tehran Prosecutor Saeed Mortazavi announced Tuesday on television that the paper's cartoonist and editor-in-chief had been detained.
"Those responsible, the cartoonist and the chief editor, were summoned and the charges were read to them. The two were taken to Evin prison," Mortazavi said.
The daily, one of the country's top three newspapers, was closed "due to its publication of divisive and provocative materials," state television reported.
Iran saw a wave of newspaper closures in past years amid the confrontation between reformers and hard-liners during the 1997-2005 presidency of reformist Mohammad Khatami. The hard-line judiciary shut more than 100 pro-reform newspapers and jailed dozens of editors and writers.
But the government of Ahmadinejad, an ultra-conservative, has taken no steps against the remaining two moderate newspapers that still publish, though they make few of the sharp criticisms of the cleric-led leadership that reformers did.
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