The former Conservative party leader Michael Howard has confronted the Israeli prime minister, Benjamin Netanyahu, over Israel’s recent killing of more than 100 Palestinian protesters, demanding to know why the country’s defence forces used live ammunition to curb the protests.

Responding to sharp, unexpected questions from one of the most prominent Jewish figures in British politics, Netanyahu said he was looking for new technological solutions to prevent protesters scaling the fence separating Gaza from Israel. He insisted the protesters were either paid civilians or Hamas members.

Netanyahu on European mission to dismantle Iran pact Read more

Netanyahu was speaking at the close of a lightning tour of Berlin, Paris and London, where he told European leaders that the Iran nuclear deal was collapsing as EU firms ended investment in Iran. The US president, Donald Trump, pulled out of the deal last month partly due to Israeli claims, rejected in Europe, that Iran was “cheating” on the 2015 deal.

Netanyahu also gave a sharp warning that the Syrian president, Bashar al-Assad, would face direct Israeli military strikes if he allowed Iran to entrench itself in Syria.

Lord Howard said many people accepted the protests had not been peaceful, but added: “Fewer people sympathise with, and understand, the proposition that the only way to stop them scaling the fence was to kill them. Why could you not use rubber bullets? Why could you – if, in extremis, you had to use live ammunition – not shoot them in the legs? Why did you have to kill them?”

The British foreign secretary, Boris Johnson, raised similar questions with Netanyahu when they met on Wednesday.

Netanyahu told Howard that the methods he proposed had been tried, and claimed: “Hamas wanted the Jews to kill more. Their goal was to have as many casualties. Our goal was to minimise casualties.”

He said he would be the first to use non-lethal means if they could be found, and insisted he was exploring other options for the future.

Facebook Twitter Pinterest Boris Johnson with Netanyahu in London at a previous meeting in 2017. Photograph: Darren Staples/AFP/Getty

He claimed his army was facing a new form of warfare. He said it was “unconscionable” that Hamas put civilians in front of its fighters as human shields. The military and political wings of Hamas were indistinguishable, he said, describing them as “the worst theocratic gangsters in the world”.

He suggested that the Hamas wings believed in nothing. “They don’t believe in democracy or pluralism. They hang gays. Why are progressive forces going behind some of the least progressive forces in the world?” The answer, he said, was antisemitism. “It is important to call things as they are.”

Netanyahu also sent out his clearest warning yet that he would not tolerate the Syrian civil war finishing with Iranians remaining inside Syria. It is an issue that increasingly preoccupies Russia as it tries to prevent Israel going to war against Assad if he allows Tehran’s influence to grow so close to Israel’s border.

In May, Israel launched a large-scale attack on what it said were Iranian targets in Syria, raising fears of a big confrontation. Those strikes followed a barrage of rockets that Israel said were fired toward its forces in the occupied Golan Heights by Iran from Syria.

Netanyahu said: “I think Mr Assad has to consider this. As long as he engages in this horrific civil war inside Syria we will not deny him a deal. Now that the war is over, and Daesh is finished, and he likes or allows Iran to come in to entrench itself with a view to attack Israel, with the intention of destroying Israel, and its sovereign territory, he is no longer immune, his regime is no longer immune.

“If he fires at us we will destroy his forces. So I think there is a new calculus that has to take place and Syria has to understand that Israel will not tolerate the Iranian military entrenchment in Syria against Israel, and the consequences are there not just to the Iranian forces, but to the Assad regime as well. I think that this is something he should consider very seriously.”

He said European leaders were very sympathetic to Israel’s desire to rid Syria of an Iranian presence, adding that this had been the chief focus of his round of conversations with European leaders.

Netanyahu also claimed that in his talks with the Russian president, Vladimir Putin, there had been an understanding that Russia would not get in Israel’s way. He said Russia was not turning a blind eye and that Moscow could see what Israel was doing.

He said the Iranian nuclear deal was “effectively defunct” regardless of European support for it, since the weight of the US sanctions was forcing firms to make a choice about whether to do business with Iran or the US. Companies were having the choose between an economy that was 3% of the size of the US economy or forgo a multi-trillion market, he said. “It is a no-brainer,” he said, “and everyone is choosing effectively as we speak. Companies are pulling out of Iran.”

By removing an incentive to do business with Iran, the US had smashed Iran’s cash machine, he claimed, adding that most European leaders recognised that the nuclear deal with Iran was falling apart.

• This article was amended on 7 June 2018 to correct the number of Palestinian deaths.

