International and domestic pressure has mounted on Israeli Prime Minister Benjamin Netanyahu as US President Joe Biden said he was not doing enough to secure the release of Gaza hostages, after the killing of six captives, AFP reports.

Britain said it would suspend some arms exports to Israel, citing a “clear risk” they could be used in a serious breach of international humanitarian law.

At a televised press conference, Netanyahu said he sought forgiveness for failing to save the six. “These murderers executed six of our hostages, they shot them in the back of the head,” he said, rejecting the idea that Israel should respond with “concessions” in Gaza ceasefire talks.

Abu Obeida, spokesman for Hamas’s armed wing the Ezzedine Al-Qassam Brigades, said remaining hostages would return “inside coffins” if Israel maintains its military pressure on Gaza.

A statement said “new instructions” had been given to fighters guarding the captives on what to do if Israeli troops approached. Late on Monday Hamas released a video that showed alive one of the six hostages whose bodies were found by Israeli forces in a Gaza tunnel at the weekend.

A strike announced by the Histadrut trade union seeking a deal to secure the remaining captives’ release brought parts of Israel to a standstill Monday, although some cities were largely unaffected.