Benjamin Netanyahu has condemned the UK government’s decision to suspend some arms export licences to Israel, describing it as a shameful decision that would embolden a genocidal Hamas.

The Israeli prime minister said his country was at war to also protect British hostages and vowed the UK measures would not prevent it from winning the conflict in Gaza.

In his first intervention since the UK foreign secretary, David Lammy, told MPs some arms export licences were being suspended, Netanyahu wrote on X: “This shameful decision will not change Israel’s determination to defeat Hamas, a genocidal terrorist organization that savagely murdered 1200 people on October 7, including 14 British citizens.”

He added: “Hamas is holding over 100 hostages, including 5 British citizens. Instead of standing with Israel, a fellow democracy defending itself against barbarism, Britain’s misguided decision will only embolden Hamas. Just as Britain’s heroic stand against the Nazis is seen today as having been vital in defending our common civilization, so too will history judge Israel’s stand against Hamas and Iran’s axis of terror.

“With or without British arms, Israel will win this war and secure our common future.”

His remarks ensure a deep diplomatic rift between Israel and the UK is likely, although Britain hasgone to lengths to explain the decision as carefully calibrated and not amounting to a full embargo, let alone a step that would weaken Israel’s security.

Netanyahu is facing unprecedented pressure over claims inside Israel that his intransigence over the ceasefire talks had indirectly led to the deaths of six Israeli hostages at the hands of Hamas.

The Labour government’s decision was facing a growing domestic backlash from all sides, with Boris Johnson accusing Labour of abandoning Israel and asking if it wanted Hamas to win the war in Gaza.

The Board of Deputies of British Jews said the decision sent the wrong message at the wrong time, while on the left there was growing anger at the loophole that would allow the UK to continue to supply parts to the F-35 fighter jet programme.

Even one of the advocates of the ban, the former national security adviser Peter Ricketts, said he left it to ministers to explain the timing of the announcement so soon after the killing of six Israeli hostages by Hamas.

In a provocative attack, Johnson, the former Conservative prime minister, said on X: “Hamas is still holding many innocent Jewish hostages while Israel tries to prevent a repeat of the 7 October massacre. Why are Lammy and Starmer abandoning Israel? Do they want Hamas to win?”

Phil Rosenberg, the president of the Board of Deputies of British Jews, criticised the government’s decision as sending a “terrible message” in Israel’s “hour of need”.

Speaking on BBC Radio 4’s Today programme, he said: “On the day that those beautiful people were being buried, kidnapped from a music festival like Reading or Glastonbury, the UK decides to send a signal that it’s Israel that it wants to penalise, and that is a terrible, terrible message to be sending both to Israel in its hour of need, also to Hamas about the consequences – where consequences are for the horrific actions that Hamas has taken as a terrorist organisation, but also to other allies and adversaries around the world. So it is the wrong decision taken very much at the wrong time.”

Asked if his decision had upset both sides of the conflict, the defence secretary, John Healey, told Radio 4’s Today programme: “This is a government with a duty to the rule of law. This is not a decision about pleasing any side in this.”

He added that the government remained resolute in Israel’s right to self-defence and the decision “will not have a material impact on Israel’s security”.

Inside the Labour party, the biggest pro-Israeli campaign group, Labour Friends of Israel, did not defend all of the Israeli government’s methods, but said: “Since 7 October, Israel has come under repeated, unprovoked and indiscriminate attack by Iran and its proxies Hamas, Hezbollah and the Houthis.

“We do not believe that restrictions on UK arms sales will help bring the tragic conflict in Gaza to a close or help ensure the release of the hostages, six of whom Hamas brutally murdered just days ago.

“Moreover, we are deeply concerned by the signal this sends to Iran, the world’s leading sponsor of state terrorism and Vladimir Putin’s closest ally in Ukraine. We fear therefore that these restrictions risk encouraging Israel’s enemies, leading to greater escalation rather than de-escalation.”

Lord Ricketts, saying he would leave it to ministers to defend the sensitive timing of the announcement, argued the government had acted to defend international law and not to influence Benjamin Netanyahu, who he said seemed impervious even to influence by its major ally the US.

He added he believed the government was concerned by the imminent prospect of judicial review, something that might undermine the whole UK arms exports control system.

Andrew Mitchell, the shadow foreign secretary and one of the ministers in the Foreign Office in the last Conservative government that shelved any arms ban, sharpened his criticism of Labour after reading the official memorandum explaining the decision to parliament.

He said: “Announcing an arms embargo on the day when Israel is burying its murdered hostages, and within weeks of British military personnel and arms defending Israel from Iranian attack, is not easy to swallow.

“Having now looked at Labour’s memorandum, it has all the appearance of something designed to satisfy Labour’s backbenches, while at the same time not offending Israel, an ally in the Middle East. I fear it will fail on both counts.”

Conservative leadership candidate Robert Jenrick said it was “shameful gesture politics to appease the hard left”.

But there was little sign the announcement had quietened the left, with the MP Zarah Sultana, currently with the whip suspended, saying: “Labour shouldn’t just ban a small fraction of arms licences to Israel. This ban still allows the UK to keep 320 arms licences including selling parts for F-35 fighter jets, known as ‘the most lethal’ in the world. The government needs to ban all arms sales.”

The large loophole of continuing to supply parts for the F-35 taken on commercial grounds and to protect British Aerospace was the subject of intense criticism.

Sacha Deshmukh, Amnesty International UK’s chief executive, said: “Exempting the F-35 fighter jet programme – essentially giving this programme a blank cheque to continue despite knowing that F-35s are being used extensively in Gaza – is a catastrophically bad decision for the future of arms control and misses a clear obligation to hold Israel accountable for its extensive war crimes and other violations.”

Campaign Against Arms Trade said the decision came just as it had become possible for the first time to confirm the F-35s’ involvement in an identifiable attack in Gaza specifically an attack on 13 July, on an Israeli-designated safe zone in al-Mawasi in southern Gaza that killed 90 people and injured at least 300.

The Israeli military said the target of the attack was Mohammed Deif, the head of Hamas’s military wing. The attack involved three GBU-31 2,000lb bombs, which have a “lethal radius” of 360 metres.

The government said it was precluding the F-35 from the 30 suspended arms export licences owing to the possible impact on the global supply chain but Sam Perlo-Freeman, the research coordinator for the Campaign Against Arms Trade, said it would have been possible to remove Israel from the list of approved recipients for the open general licence. “Exempting parts for Israel’s F-35 is utterly outrageous and unjustifiable.” he said.

The brief assessment published by the government said it had been the treatment of Palestinian prisoners and the inadequate supply of humanitarian aid, not the destruction of Gaza, that represented the two clearest breaches of international humanitarian law (IHL).

It added that it was the overall Israeli approach to IHL revealed over these two issues that led ministers to believe there was a clear risk that British arms would be used to commit a serious breach.