Iran was rocked this week by the largest protests in the country since 2009.

Pro- and anti-government demonstrators took to the streets starting Thursday and gradually moved from the outer cities into the capital, Tehran, and Iran's second-largest city, Mashhad.

At least 20 people were dead as of Tuesday morning. As of Monday, six people were dead in the small city of Tuyserkan, two in the city of Dorud, two in the southwestern city of Izeh, and two in Lorestan province.

The protests have attracted global attention, and footage of the action has been shared hundreds of thousands of time on social media.

The demonstrations became so widely publicized that Iran blocked access to Instagram and a popular messaging app used by activists to organize and discuss the protests.

Here's what you need to know about the demonstrations: