Israeli Prime Minister Benjamin Netanyahu sought Britain's cooperation to "turn back the tide of militant Islam" as he met Prime Minister David Cameron in London on Thursday.
"The Middle East is disintegrating under the twin forces of militant Islam: The militant Sunnis led by ISIS and the militant Shiites led by Iran," said Netanyahu, using an acronym for the Islamic State jihadist group, as he began talks with Cameron at Downing Street.
"And I believe that we can cooperate in practical ways to roll back the tide of militant Islam both in the Middle East and in Africa altogether."
A Downing Street spokesman said the two leaders discussed the threat of Islamist extremism and pledged to work together on cyber-security.
They agreed "a new package of co-operation covering training and joint exercises to prepare against cyber attacks", the spokesman said, adding that Britain would send "a cyber business delegation" to Israel in December.
"If we pull our resources together we can offer a better future and great prosperity," said Netanyahu, hailing Israel as a "global hub of innovation" in cyber security.
On the Israeli-Palestinian issue, the Israeli leader said he was willing to resume negotiations "immediately" with the Palestinians, "with no conditions whatsoever".
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His visit was preceded by clashes between pro-Palestinian and pro-Israeli protesters outside Downing Street on Wednesday with police breaking up the scuffles as around 500 protesters gathered, waving placards and flags.
Both leaders "reiterated their commitment to a two state resolution", Downing Street said, adding: "The prime minister emphasised the importance of improving daily life for the people of Gaza, for example through better power and water supplies and facilitating travel in and out of Gaza."
Ahead of the visit more than 108,000 people signed a petition urging Netanyahu's arrest for war crimes in relation to the 2014 Gaza conflict, enough for the issue to be considered for debate in Britain's parliament.
Israel's embassy in London called it a "meaningless publicity stunt".
Iran was also on the agenda at Thursday's meeting, with Netanyahu reiterating his criticism of the nuclear deal agreed with western powers in July as he touched down in the British capital on Wednesday.
"All responsible countries must cooperate in order to stop Iran's terrorism and aggression which, to my regret, will only increase as a result of the agreement," he said.
Downing Street said the two leaders recognised there were "differences in their approach" but "both shared the objective of greater stability in the region, and agreed it was in the interests of all that Iran allowed regular inspections of its nuclear facilities."