A screengrab from the terrorist leader’s video

Al-Qaeda leader Ayman al-Zawahri has warned the United States of the “gravest consequences” if Boston marathon bomber Dzhokhar Tsarnaev or any other Muslim prisoner is executed.

Tsarnaev, named in a new online video message from Zawahri, was sentenced last year to death by lethal injection for the 2013 bomb attack, which killed three people and injured more than 260.

“If the U.S. administration kills our brother the hero Dzhokhar Tsarnaev or any Muslim, it … will bring America’s nationals the gravest consequences,” Zawahri said.

The nearly hour-long video, which included images of Tsarnaev, gave no indication of the location of Zawahri, believed to be based close to the Afghan-Pakistan border.

Tsarnaev carried out the Boston bombings along with his older brother Tamerlan, who was killed in a confrontation with police soon after. No organization claimed responsibility.

Legal wrangling over Tsarnaev’s fate could play out for years or even decades. Just three of the 74 people sentenced to death in the United States for federal crimes since 1998 have been executed.