“I say that because we also have news reports now coming in that the US and UK warships are headed into the Mediterranean. On one of the US ships is probably a Marine Expeditionary Unit,” Johnson said. 

“This is extremely dangerous. […] This attack [on Haniyeh] was so blatant that I don't think there will be any restraint on the part of Iran or Hezbollah. I think that this may in fact have been crossing a red line. It is extremely worrisome because this has the hallmarks of being able to spin out of control. And it is, we're now in a situation of wait and see,” Johnson stressed.

"We are paying increased attention to the incident; we strongly oppose and condemn the murder, and are deeply concerned that this incident could lead to greater instability of the situation in the region,"Chinese Foreign Ministry Spokesman Lin Jian said.

"The Islamic Republic of Iran will defend its territorial integrity, dignity and honor, by making the terrorist occupiers regret their cowardly act," Pezeshkian said, as cited by the Tasnim agency.

“The Israeli army carried out the operation after receiving the "green light" from the United States, and responsibility for its consequences rests with both Israel and the American administration. They committed this murder to exert pressure on Hamas, and to force us to accept their negotiation terms - which we reject. We affirm that the Israeli army will pay dearly for this crime," he said.

“The martyrdom of Haniyeh will only strengthen the movement's resolve to resist aggression, and will not weaken the support Hamas provides to the resistance (force) against the Israeli enemy. The killings of our leaders have never stopped us in the past. All options and scenarios for responding to this murder are possible, and the current developments, including a strike on Beirut, could lead to a large-scale regional war - for which Washington will also be held accountable," Taha concluded.

"The criminal terrorist Israeli regime killed our dear guest in our house and [forced us to] grieve, but it also prepared the ground for its harsh punishment," Khamenei was quoted as saying by the IRNA news agency.

"The increased military buildup by the US and Japan in the Asia-Pacific region means a greater risk for war, particularly nuclear war," Hawaiian activist with Okinawan roots Robert Kajiwara tells Sputnik.

"If there's any country that should be against nuclear arms, it should be Japan, given the use of nuclear weapons against the cities of Hiroshima and Nagasaki. Japan should be strongly against the storing of nuclear weapons in its territory. Unfortunately Japan hasn't learned anything from World War II and appears destined to repeat its past mistakes," Kajiwara concludes.