KABUL - With most foreign combat troops set to withdraw from Afghanistan by 2014, Iran is is using the media in the war-ravaged nation to gain influence, a worrying issue for Washington.

Nearly a third of Afghanistan's media is backed by Iran, either financially or through providing content, Afghan officials and media groups say.

"What Iran wants, what they are striving at, is a power base in Afghanistan that can counter American influence," said a senior government official, who like others for this report, spoke to Reuters on condition of anonymity.

"They are without a doubt doing this through supporting and funding our media."

Iran spends $100 million a year in Afghanistan, much of it on the media, civil society projects and religious schools, says Daud Moradian, a former foreign ministry adviser who now teaches at the American University in Kabul.

"It is using Afghanistan to send a message to America that it can't be messed with. Afghanistan becomes a managed battlefield as a result."

Officials in Tehran could not be reached for comment despite repeated attempts and the Iranian embassy in Kabul said it was not prepared to talk about the issues raised in this report.

The landmark agreement NATO leaders sealed this week in Chicago, handing control of Afghanistan over to its own security forces by the middle of next year, puts the Western alliance on an "irreversible" path out of the unpopular, decade-long war.

Some security analysts say the withdrawal could lead to increasing instability and then to civil war -- and an opportunity for Iran and others to move into the resulting power vacuum.

When the Soviet Union withdrew from Afghanistan in 1989 following a decade-long occupation and the pro-Moscow government in Kabul collapsed, Afghanistan's neighbors moved in to arm and fund proxies to gain regional influence as the country plunged into civil war.

Although Kabul's ties with Tehran have seen sporadic improvement after the 2001 ouster of the Taliban, which had emerged triumphant after the civil war, the relationship is combustible.

The latest flashpoint is the recent signing of a long-term strategic agreement between the United States and Afghanistan. Though vague on details, the pact was meant to signal US financial and security commitments to Afghanistan through 2024 - particularly for funding the large Afghan National Army.

Iran, whose frayed ties with the United States have worsened over its disputed nuclear program, sees the pact as a threat. Iranian-backed media in Afghanistan responded by churning out reports critical of the agreement, and Tehran's ambassador to Afghanistan Abu Fazel Zohrawand threatened to expel Iran's one million Afghan refugees if the pact was not rejected.

Afghanistan's intelligence department, the National Directorate of Security (NDS), had earlier gone public with Iran's alleged meddling in the media, saying that weekly newspaper Ensaf and TV channels Tamadon and Noor had received financial support from Iran.

A journalist who recently left Tamadon TV, owned by Afghanistan's most prominent Shi'ite cleric Ayatollah Mohammed Asef Mohseni, told Reuters that while the station never confirmed it was getting support from Tehran "it was obvious".

"My salary of $600 a month would fluctuate dramatically, as it was pegged to Iran's rial," said the 23-year-old, one of 200 employees at Tamadon, where he worked for four years before resigning over fears his employment would land him in trouble with Afghan authorities.

"Our office is full of posters calling for protests against the strategic pact with America. We'd invite pro-Iran analysts onto our shows saying Iran was the only one who could help Afghanistan with food and supplies," said the recent graduate, dressed in a tight black long-sleeved t-shirt and jeans.

Tamadon TV dismissed the claims of Iranian backing as an "insult". Editor in chief Mohammad Rahmati said the station was targeted "because we show core Islamic values; we don't show half-naked dancing women".

Afghanistan has been so much a focus of big power rivalry over the past 200 years -- a failed British occupation in the mid-19th century, the failed Russian one in the 1980s, for example -- it has its own historical sobriquet, "The Great Game".

As the United States prepares for its own dispirited withdrawal from Afghanistan, it is worried about Iran gaining a strategic advantage in Afghanistan, after seeing Tehran win influence in Iraq following the 2003 US invasion.

More than half of the 171 TV, satellite channels and radio stations licensed to broadcast in Iraq today are funded by Iran, with others backed by the United States and Arabic Gulf countries, government communications officials say.

Iran's media strategy is but one strand in a multi-pronged projection of "soft power" into Afghanistan. The two countries share cultural, language and historical links -- for centuries they were part of the ancient Persian empire -- as well as a long and porous border.

Iran said in 2010 it has provided some $500 million in official assistance for reconstruction projects. Tehran has built religious schools for Afghan Shi'ites, who comprise a fifth of Sunni-majority Afghanistan's 30 million people.

Iran may even have MPs on its payroll. An Afghan official who declined to be identified told Reuters that up to 44 of the 249 members of the Afghan parliament are suspected of receiving money from Iran. Iran has not responded to those allegations, which have also been aired in the Afghan media.

Iran's vehement opposition to the new strategic pact with the United States appears to have intensified efforts to influence public opinion about it.

Ensaf newspaper, one of the three media outlets the government has said receives funding from Iran, and whose parent company Avapress has offices in Tehran, has published six critical articles on the pact since it was signed by President Barack Obama on a whistlestop visit to Kabul on May 2.

The three media outlets feature news reports that hold little interest for Afghans, but are important to Iran, using the same messages and wordage carried by Iranian state media.

The state of Israel, for instance, is called "the Zionist regime", a term Afghan officials generally avoid using.

"The fact is the stories broadcast have been made available by Iranian sources for propaganda purposes", Loftullah Mashal, a spokesman for the intelligence agency NDS, said last month. The NDS later retracted that claim.

Iran first started attempting to influence Afghan affairs through the media in 2006, said Abdul Mujeeb Khalvatgar, executive director of the Afghan media development group Nai.

"The pace has been quickening since 2011, which is when Iran began to actually inject its viewpoint into Afghan media," he said.

Last year, Afghans were shocked when Tamadon TV broadcast a live speech by Iran's parliament speaker Ali Larijani criticising the presence of Western troops in Afghanistan.

Kabul is countering with its own pressure.

The Kabul-based reporter of Iran's semi-official Fars News Agency, Abdul Hakimi, was arrested two weeks ago on charges of spying, Afghan officials said. The NDS declined to comment.

The relatively large, often Western-backed press corps can also face intimidation, abduction or even death for reporting on issues such as corruption and other government failings. Afghanistan ranks seventh on the Committee to Protect Journalists' "Impunity Index", a listing of countries where journalists are killed regularly and governments fail to solve the crimes.

One man who says he is painfully familiar with Iranian interference is author and journalist Razaq Mamoon. He says a masked man who threw acid in his face in January of last year was working for Tehran. The Iranian embassy in Kabul has not commented on his allegations.

Though media reports at the time said his assailant staged the attack over a soured love affair, Mamoon says his 2010 book which accuses Iran of sabotage and espionage in Afghanistan, motivated Iranian intelligence agencies to attack him.

"Those individuals who planned the attack on me are still in power and their Iranian spy agencies are still very active in Kabul," Mamoon, who now lives in New Delhi out of fear for his safety, told Reuters in e-mailed comments.

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