Action is needed to stop the Middle East “disintegrating” under the threat of militant Islamists, Israeli PM Benjamin Netanyahu said at the start of talks in London with David Cameron.
Discussions are set to focus on Syria and Iran, particularly the nuclear deal bitterly opposed by Mr Netanyahu.
Mr Cameron said the UK “remains staunch” in its “defence of Israel’s right to exist and to defend itself”.
Pro-Palestinian campaigners have denounced Netanyahu’s visit.
There were confrontations outside Downing Street on Wednesday between protesters demanding Mr Netanyahu’s arrest for war crimes in Gaza and pro-Israel activists.
Although a petition calling for the Israeli PM’s arrest secured enough signatures to be considered for a debate in Parliament, the bid was rejected earlier this week because “visiting heads of foreign governments… have immunity from legal process, and cannot be arrested or detained”, the UK government said in a statement.