The escalating crisis in Lebanon and legal difficulties in defining UK arms exports used solely for offensive purposes has prompted Britain to delay making a decision on banning some arms sales to Israel. It is now likely the decision will be deferred for several weeks, after a rocket attack on the Golan Heights this weekend, killing 12 people, triggered Israeli retaliation in Lebanon. In a statement to MPs, the foreign secretary, David Lammy, called for restraint by all sides, advised against all travel to Lebanon and warned the consequences of a wider conflict would be “catastrophic”. He added: “We support Israel’s right to defend itself in line with international humanitarian law. They are in a tough neighbourhood threatened by those that want to annihilate it.” Warning Iran was stoking tension, he added: “For months now we have been teetering on the brink. The risk of further escalation and regional stabilisation is now more acute than ever.” Lammy has said that in terms of a sales suspension he wants to make a distinction between weapons used by Israel for the war in Gaza and those used defensively. But at a time when Israel is facing missile attacks from Hezbollah in Lebanon, this distinction is proving harder to draw in law, as well as politically challenging. Ministers for instance will need to decide how to categorise UK components used by Israel in the F-35 jet planes it has bought from Lockheed Martin in the US. A ban on F-35s parts would be resisted by BAE Systems, but the F-35s have been used to mount attacks in Gaza, as well as defend Israel. The shadow foreign secretary, Andrew Mitchell, called for caution on an arms sales ban, urging Lammy to “remember that just a few weeks ago, British arms and military personnel were defending our ally Israel, from missiles launched by Iran”. Answering questions in the Commons, Lammy told MPs the test on arms sales was whether there was a clear risk of a breach of international humanitarian law, something he said he would address “with sobriety and integrity”. He said he had been under an obligation to commission fresh legal advice, but said there would be no step by step abandonment of Israel as an ally, as some Tory MPs claim. Asked if the legal advice would be published once it was completed, the development minister Anneliese Dodds said the foreign secretary would be “as transparent as he possibly can”. The new Middle East minister, Hamish Falconer, also sent a warning to Israel about the continued expansion of Israeli settlements on the West Bank, pointing out more land had been declared as state land this year than at any time since the Oslo accords 30 years ago. The UK has already imposed sanctions on eight individuals and two entities over settlements, he said, adding “we will be looking at all options’’. Dodds in particular indicated she believed humanitarian law was not being followed, saying: “Too many people have died in Gaza and too little aid is getting in.” “We are clear that Israel must take concrete steps to protect civilians and aid workers in accordance with international humanitarian law,” she said. “This includes deconfliction between military and humanitarian operations, and supporting the minimum operating requirements of the UN agencies.” Labour has already restored £21m funding to the UN relief works agency Unrwa. Lammy was not asked about the reports of systematic maltreatment of Palestinian detainees, but the UK has for months been pressing the Israelis to allow independent UK lawyers inside the prisons to examine allegations of torture. The treatment of the detainees, by being a reflection of Israel’s human rights record, can be another factor in deciding whether arms sales can proceed. Organisations Human Rights Watch (HRW), ActionAid UK and Oxfam accused the government of engaging in “legal gymnastics” and having “dithered once again” over the banning of arms sales to Israel. Yasmine Ahmed, the UK director of HRW, called the decision to suspend arms sales a “critical next step”. “It is disappointing that the government appears to be dragging its heels,” she said. “The longer this decision takes, the more damage the government is doing to its reputation.” “The government is fully aware of the risk that arms exported from the UK are likely being used to commit war crimes in Gaza,” said Halima Begum, Oxfam GB’s chief executive. “By selling F-35 components to Israel, the UK government is effectively facilitating many of the Israeli airstrikes and the decimation of Gaza.”