This visit comes after the assassination of Ismail Haniyeh, the chief of Hamas’ political bureau, in Iran last Wednesday and the high-profile assassination of Hezbollah’s senior military commander Fuad Shukur in southern Beirut late Tuesday.

Russia's Zvezda TV channel aired video footage, showing the Russian secretary meeting with Rear Admiral Ali Akbar Ahmadian, a senior member of Iran’s Revolutionary Guard. 

"In Tehran, the secretary of the Russian Security Council is scheduled to meet the president, the secretary of the Supreme National Security Council, and the head of the General Staff," said Zvezda. 

Pezeshkian vowed Wednesday to make Israel "regret" the "cowardly" assassination of Hamas political leader Ismail Haniyeh in Tehran. 

"The Islamic Republic of Iran will defend its territorial integrity, honour, pride, and dignity and make the terrorist invaders regret their cowardly action," said Pezeshkian in a post on X, where he mourned Haniyeh as "a brave leader."

Iran's supreme leader Ayatollah Ali Khamenei vowed "harsh punishment" for Israel after the killing of Haniyeh in Tehran.

Russia has condemned the assassination of the senior Hamas leader in Tehran while calling on all parties to refrain from any escalation that could plunge the region into all-out war. 

Diplomatic efforts to stop wider war
 

US Secretary of State Antony Blinken told his counterparts from the G7 nations in a conference call on Sunday that any attack, which he expected to be a joint undertaking between Hezbollah and Iran, could happen within 24 to 48 hours, as early as Monday, US news site Axios reported.

Blinken asked his counterparts to place diplomatic pressure on Tehran, Hezbollah, and Israel to "maintain maximum restraint," it added.

Experts and diplomats fear that the expected retaliatory attack on Israel could rapidly spiral into a regional war.

Turkey on Monday joined multiple Western and other nations calling on their citizens to leave Lebanon, where Hezbollah is based.

Flights stop bracing for attack
 

Numerous airlines have suspended flights to Israel, Lebanon, and Iran or limited them to daylight hours.

Germany's Lufthansa, which has already suspended flights to the region including Tel Aviv, said its planes would avoid Iraqi and Iranian airspace until at least 7 August.

Fearing further attacks, flights to Beirut by Air France and low-cost carrier Transavia France have been suspended. 

150,000 Israelis have been stranded in international airports as flights have also been suspended to Tel Aviv, reported Israel's Channel 12 on Sunday. 

Last Wednesday, the Israel Aviation Authority said it had cancelled flights to and from Israel until midnight. Israel also closed airspace from Hadera city, north of Tel Aviv, to the northern border.