The Syrian rebel fighter pulled a small copper-plated bullet from his trouser pocket, offering it as supporting evidence as he levelled charges of Iranian involvement in President Bashar al-Assad's army crackdown.

These are what they are firing on us, rebel fighter Ayham told Reuters outside the Reyhanli refugee camp in Turkey's southern Hatay province, where thousands of Syrians have fled.

These are Iranian bullets. I have done my military service, I know the Syrian army does not use these bullets, he said.

It might be little more than a wild guess, but it says a lot about people's view of Iran hereabouts, one clearly shared in Western capitals.

During a U.N. Security Council briefing last week, the United States and Britain accused Iran of shipping weapons to Syria they said were being used against the Syrian people.

American and European security officials say Iran provides a broad array of assistance to Assad to help suppress anti-government protests, including high-tech surveillance technology.

Iranian security officials have also travelled to Syria to advise Assad how to counter dissent, they said, with some staying on in Syria to advise Assad's forces.

It might need a ballistics expert to say where the bullet Ayham showed had come from, but Syrians speak Arabic, and witnesses told Reuters some of the gunmen operating alongside Assad's army were speaking another language. Not knowing Farsi, they could not identify that language, but made their own assumptions.

DESERTERS

It is just Syrian soldiers shooting at us, they have Iranians fighting with them too, said 23-year-old Khaled, another fighter in Reyhanli, overlooking the border with his homeland.

The men did not look like local people, from the village, in the way they dressed or comported themselves.

We know they are Iranian, because they look Iranian and they are not speaking Arabic, he said.

Khaled said he was a fighter in the Free Syrian Army, a loose alliance of army deserters and civilians who have taken up arms against Assad. He said he had crossed back into Turkey last week.

Though the accusations against Iran have been around since the early days of the one-year-old uprising, they are hard to verify as the Syrian government does not allow independent journalists and rights groups to enter Syria, except under closely controlled conditions.

If looks were everything it would be easier to trust their word; but true or not, the widespread antipathy toward Iran among Syrians who have fled to Turkey was undeniable.

The stories of Iranian gunmen and Iranian arms supplies for Assad are common currency among rebel fighters, refugees and activists.

Iran has for decades been a patron to Syria, which has helped funnel aid and weapons to the Iranian-backed Shi'ite Muslim militia Hezbollah in Lebanon.

Shi'ite Muslim Iran backed popular uprisings which have removed leaders in Egypt, Libya and Yemen but has steadfastly supported Assad, who is a member of the minority Alawite sect, an offshoot of Shi'ite Islam.

The majority of Syrians are Sunni, like those who have fled the country.

Hatay sits straight across the border from the northwest Syrian province of Idlib, where security forces have mounted increasingly heavy attacks on neighbourhoods where anti-Assad sentiment runs high.

Mohammad, a 35-year-old farmer who had fled two weeks ago with his family from Killi in Idlib just across the border, said he had seen Iranian plain clothes officials in his village.

I know they were from Iran because they do not look like us and they were not speaking Arabic. They wear civilian clothes but they are working with the Syrian secret police, said Mohammad. Iran is supporting Assad and his army.

In Hatay region's main city Antakya, a 65-year-old Syrian activist from Jisr al-Shughour, who collects non-lethal aid to be smuggled to rebel fighters in Syria, did not mince his words.

Show me an Iranian and I will cut him, he said, motioning his hand across his throat. The activist declined to be named.

REGIONAL RISK

Iran's applause for Assad's methods of countering the threat to his rule stands in plain view.

Earlier this week, Iranian media reported President Mahmoud Ahmadinejad's praise for the Syrian leadership's handling of the year-long uprising and his promise to do everything possible to support the Syrian government.

The United Nations says more than 9,000 people have died in the crackdown. Syrian authorities, who blame foreign-backed terrorists for the violence, say 3,000 soldiers and police have been killed.

There are more than 17,000 Syrian refugees now living in tented camps in Turkey near the Syrian border with 200 to 300 arriving every day.

Under U.N. sanctions imposed on Iran for refusing to halt its nuclear enrichment program, Tehran is banned from exporting weapons.

Iran and Syria have denied charges of arms trade and this week, Damascus told the United Nations armed terrorist groups in Syria were receiving weapons from supporters in Lebanon and other states along the Syrian border.

There had been a time when Iran and Turkey vied for influence over Damascus; but Prime Minister Tayyip Erdogan soon learned that when Assad's back was to the wall, it was Tehran he turned to rather than listen to Ankara's advice to reform and halt attacks on protesters.

Ditching his old friend, Erdogan has come out strongly in support of Syrians who have risen against Assad.

In a complex region, Turkey, whose Muslims are mostly Sunni, has carefully tried to stay on good terms with Iran, despite being a member of the western NATO alliance. Erdogan visited Iran on Wednesday for talks dominated by how to end the conflict in Syria.

Turkey has been telling Iran privately for months to use its influence to persuade Assad to step down.

The fear for Turkish leaders is that Syria's internal conflict could develop into a sectarian, ethnic conflict that could spill across borders, pitting Shi'ite Muslims against Sunni.

(Editing by Simon Cameron-Moore and Ralph Boulton)