The Chief of Staff of the Iranian Armed Forces Major General Mohammad Bagheri made the remarks on the sidelines of the the funeral of Hamas' Political Bureau Chief Ismail Haniyeh in Tehran on Thursday.

"Various actions must be taken and the Zionists will surely regret," General Bagheri said.

"We are investigating the way of taking revenge. This will definitely happen."

Ismail Haniyeh, the political bureau chief of the Palestinian resistance movement Hamas, and one of his bodyguards were killed in their residence in the Iranian capital early on Wednesday.

They were killed after their residence was hit, the public relations office of the Islamic Revolution Guards Corps (IRGC) said in a statement.

The reasons behind the attack are under investigation and the details will be released later, the statement read.

Haniyeh was in Tehran to attend the inauguration ceremony of the new Iranian President Masoud Pezeshkian on Tuesday (July 30).