Yusuf Yazdi is a professor of biomedical engineering at Johns Hopkins University.

He is also the son of Iranian parents. Over the holidays, he went to visit his mother in Tehran.

In the neighborhood where my mother's house is, there is a large square there and a large group.

He was telling NPR Steve Enskeep about his experience.

There was about 2, 300 young people mainly, a few older folks like me and then mostly younger

people.

And they're very peaceful, chanting slogans, mostly, you know, death to the dictator.

A few people, maybe five, he estimates, were more active in leading the chance.

And they pulled some pavers up from the sidewalk and started throwing him at the riot police.

And then the riot police responded with tear gas.

At this point, Yusuf Yazdi made what he called a mistake.

I made the mistake of breathing a bit through my mouth, which you kids, lesson learned, never breathe through

your mouth if you're experiencing tear gas attack because your throat will burn for days and still

kind of irritating. This was early in the current wave of protests. What began as demonstrations

against the economic crisis have become a broader anti-government movement in cities and towns across Iran.

You know, it seemed like a government that has run out of steam. I couldn't find anybody that

has anything nice to say about the way things are being run, whether they're pro-government or

anti-government. Iran's authoritarian government has responded with more than tear gas and batons.

More than 2,500 people have been killed. That's according to the U.S.-based human rights activist news agency,

NPR has not been able to independently verify that number. The U.S. has been weighing military responses,

and according to a U.S. official not authorized to speak publicly,

some American military personnel are now confirmed to be leaving an air base in Qatar, a possible

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