Iran’s acting foreign minister reiterated the country’s determination to punish Israel for last month’s killing of a top Hamas leader in Tehran.

“The Islamic Republic of Iran will make Israel’s violations costly for this transgressive regime in a legitimate and resolute measure,” Ali Bagheri-Kani said, according to a statement released by Iran’s foreign ministry early Sunday. He did not disclose specifics on the potential scale or timing of the planned retaliation.

Ali Bagheri-Kani made the remarks during a phone call with Belgian Foreign Minister Hadja Lahbib, according to the statement. He emphasized that Iran’s response will be “in line with defending its national security, territorial integrity and sovereignty, and based on international law, global norms, and the United Nations Charter.”

The remarks add to an escalating series of statements from Iranian officials saying that revenge for the assassination of Hamas political chief Ismail Haniyeh is inevitable.

Haniyeh was in the Iranian capital to attend the inauguration of President Masoud Pezeshkian when he was killed by a strike on his guest house overnight. Israel has neither confirmed nor denied responsibility for his death.