Several television and radio channels of Iran’s state broadcaster were hacked Thursday with photos of leaders of an opposition group briefly aired.

The image of Massoud and Maryam Rajavi, leaders of the Albania-based opposition Mujahideen-e Khalq (MEK), were broadcast for around 10 seconds with audio footage from one of their speeches in the background.

Massoud Rajavi disappeared during the 2003 invasion of Iraq, where the MEK was then based in alliance with Saddam Hussein, and is widely believed dead.

After the picture of the MEK leaders, the video showed a photo of Iran’s Supreme leader Ali Khamenei with a red cross on it, as an off-camera voice said, “Death to Khamenei.” It was unclear whether this was a recording of slogans chanted during protests. Khamenei was badly injured in 1981 in one of a series of bombings attributed to the MEK.

There was also a red circle on the video, which called for an uprising in Iran to overthrow the current regime. The video then cut into footage of a snowy screen disturbance that is usually aired on TV when there is a technical problem.

The first channel of the national TV and several popular radio channels as well as a website for the online streaming of IRIB channels were targets of the hack. The state broadcaster’s deputy for technology, Reza Alidadi, said the hackers probably accessed IRIB servers, adding that the “complicated attack” was under investigation.