The leader of Hezbollah on Thursday said this week’s deadly attack on the Lebanon-based militant group’s communications devices was a “severe blow” that crossed a “red line”.

Hassan Nasrallah said the group is investigating the two-day attack, which killed more than 35, wounded thousands and was widely believed to be carried out by Israel.

“Yes, we were subjected to a huge and severe blow,” Nasrallah said. “The enemy crossed all boundaries and red lines.”

As usual, Nasrallah spoke by video from an undisclosed location. Hezbollah typically convenes a rally for supporters to watch his speeches on a big screen, but this time they did not.

Hundreds of electronic devices used by Hezbollah exploded in Lebanon earlier this week, killing at least 37 people and wounding some 3,000 others.