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Iran's anti-U.S. venom masks hardliners' unease

Tehran It is no coincidence that this year, with U.S.-Iranian relations as cordial as they've been in decades, a record crowd filled the streets outside the former U.S. Embassy in Tehran to shout "Death to America."

In fact, it was difficult to get through the mass of people and the beefed up security which included -- for the first time -- metal detectors.

November 4 is the anniversary of the takeover of the U.S. Embassy by radical Iranian students 34 years.

Every year, a ritual anti-U.S. protest takes place outside the former U.S. compound (which has been turned into a Revolutionary Guard training college).

With tens of thousands joining the protests, this year's was the biggest and liveliest gathering in years -- possibly since the takeover itself. Of course, it didn't happen spontaneously. Hardliners in the Iranian regime, especially in the security forces, organized the show by mobilizing loyal supporters.

It's a measure of how worried they are.

The current talks underway with the United States could see Iran making concessions in its nuclear program in return for improved political and business ties with the U.S. and Europe. Something that looked impossible just five years ago now looks distinctly within reach.

But improved relations would undermine the hardliners. They would be forced to swap demonization for cooperation, and the cozy financial empires they've built would be under threat.

This morning's demonstration, while large, was basically a repeat of the old tropes: "Death to America" chants, burning American flags, and street theater ridiculing the presidents of the U.S. and Israel.

But there was one new sign, tellingly inspired directly by the Iran-U.S. negotiations, which are due to resume later this week.

It shows an Iranian and an American face to face at a negotiating table. The American wears a business suit on top, but under the table and out of view to his negotiating partner, he's carrying a gun, and wearing combat pants. The message is obvious -- Americans are violent and untrustworthy.

Two weeks ago, that same image was put up on billboards all over Tehran. Then suddenly, they were all taken down again by official order.

Along with the size of today's demonstration, the signs appearing and promptly disappearing are visible indications of the ferocious power struggle taking place inside the Iranian regime.

The new president, Hassan Rouhani, and his entourage believe Iran's best interests -- and their own -- will be served by restoring long-severed links with the U.S. and the West. They're bitterly opposed by conservatives who think this strategy will spell the end of the Islamic Republic.

Perhaps, by November 4 a year from now, we'll have a better idea of who's winning.

Filed by CBS News' Seyed Bathaei in Tehran, and Elizabeth Palmer in London.