The Israeli military said it struck Iran early on Friday morning, attacking dozens of military targets, including nuclear sites, in different areas of the country.

The scale of the attacks and the damage they caused were not immediately clear. But the strikes raised fears that the long-simmering conflict between the two countries could escalate into an all-out war involving the most two powerful militaries in the Middle East.

Here’s what to know about the situation:

What happened in Iran?

Explosions rocked Iran’s capital, Tehran, early on Friday. Iran’s state media showed blasts across the city, with smoke and fire billowing from buildings. The skies were quickly cleared of civilian flights.

Mohammad Jamali, who was standing on a roof in Tehran, said he could see two Israeli jets attacking an air base of the Revolutionary Guards. “What I can see is two massive flames and smoke coming from two military bases in eastern Tehran,” he said.

A senior Iranian official said that a compound in Tehran where senior military commanders live, Shahrak Shahid Mahalati, had been attacked, and that three residential buildings had been demolished.