Story highlights Billboards with anti-U.S. slogans are collected in Iranian capital, state news reports

Those who put them didn't have permission from Tehran authorities, spokesman says

This comes amid a thaw in U.S.-Iran relations, though tension and differences remain

Anti-American sentiment is nothing new in Iran. But what about government officials ordering that billboards expressing such views be taken down?

That's what is happening in Tehran, where billboards bearing anti-U.S. slogans were collected, according to the state-run Islamic Republic News Agency

Hadi Ayazi, a spokesman for Tehran municipality, told reporters that a cultural institute had installed the billboards without the consent of Tehran municipality's cultural council, IRNA reports.

The move comes during a seeming thaw in U.S.-Iran relations, amid ongoing talks over the latter's nuclear program. U.S. President Barack Obama and Iranian Hassan Rouhani have even exchanged letters, with both signaling openness to further improvement.

Still, like the stringent U.S.-led sanctions imposed on Iran, the animosity and tension aren't entirely gone.

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On the same English-language front page of IRNA, for instance, there was a story in which Ali Larijani, speaker of Iran's Parliament, criticized "some talkative creatures" in U.S. politics for criticizing Iran and its involvement in a possible political solution in Syria.