Terrorists seizing anti-aircraft and chemical weapons could be "game changers" in the Middle East, Netanyahu told the BBC in an interview broadcast Thursday. He was in London to attend the funeral of former British Prime Minister Margaret Thatcher on Wednesday.
Israel's policy is not to get involved in the Syrian conflict, but in recent months it has retaliated against Syrian gunfire spilling into Israeli-controlled areas in the Golan Heights.
There is an international push for countries to directly arm rebel fighters in their drive to oust Syrian President Bashar Assad from power.
"The main arms of concern to us are the arms that are already in Syria -- these are antiaircraft weapons, these are chemical weapons and other very, very dangerous weapons that could be game changers," he told the BBC.
"They will change the conditions, the balance of power in the Middle East," the prime minister explained. "They could present a terrorist threat on a worldwide scale. It is definitely our interest to defend ourselves, but we also think it is in the interest of other countries."
"We don't seek military confrontation, but we are prepared to defend ourselves if the need arises," he said.
Netanyahu also repeated his view Iran and its nuclear program are a direct threat to world peace. He said it would not be stopped by sanctions or hard-hitting diplomacy but by "direct military threat."
"Other countries, once they see Iran getting nuclear weapons, will rush to get their own nuclear weapons and then the Middle East will become a tinderbox," he told the BBC.
The North Korean crisis had demonstrated for world leaders what could happen when a rogue state acquired nuclear weapons, the Israeli leader said.
"Iran is many times stronger than North Korea, both in [gross domestic product] and aggressive tendencies," he said. "I think there's an interesting change of perception because people can understand what it would be like to have Iran with their imperial ambitions, with their messianic and apocalyptic ideology possess atomic bombs."