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By Ali Arouzi and F. Brinley Bruton

TEHRAN — Huge crowds chanted anti-Israel and U.S. slogans in Iran's capital on Friday, an indication of the power that hardliners still hold even as negotiators struggle to finalize a nuclear deal that would help normalize the country's relations with the rest of the world.

"Today, I am here to punch Israel in the mouth," said Fatemeh Hossieni, a 61-year-old English teacher who was marching for Al-Quds Day, a holiday held to show support for Palestinians. "Israel will be destroyed, America will be destroyed — so will ISIS and England."

Negotiators for Iran and six world powers — the U.S., Britain, Russia, China, Germany and France — have missed a series of deadlines trying to craft a deal that would restrict Tehran's nuclear program in exchange for easing punishing economic sanctions.

On Friday, as talks reportedly became fractious, Iran's Foreign Minister Mohammad Javad Zarif dismissed warnings that the U.S. was ready to leave the talks, saying they were counterproductive. The negotiations in Vienna were later extended until Monday afternoon.

But Hassan Khanalizadeh, a 26-year-old journalist, vowed that even if the negotiators succeeded, Israel would still be vulnerable.

Related: Nuclear Deal Must 'Stand the Test of Time,' Kerry Says

"I am here to stand by the Supreme Leader's words. With or without a deal Israeli security will never be safe," he said, referring to the country's most powerful man, Ali Khamenei.

The Iranian leader has walked a fine line between supporting his negotiators while also maintaining the peace with the country's conservative forces, who are opposed to a pact.

The U.S.'s close ally, Israel, is dead set against a deal. It says Tehran should not be allowed to enrich any uranium — as envisioned under the agreement that is being negotiated.

Israeli Prime Minister Netanyahu has railed against the deal, saying Iran cannot be trusted. In March, he delivered a scathing speech to the U.S. Congress in an attempt to derail the process.

Associated Press contributed.