Francois Hollande's message was sure to be welcomed by his Israeli hosts, who have voiced concerns that an emerging deal with global powers gives Iran too much without getting enough in return.
"France will not make concessions on nuclear proliferation," Hollande said at a welcome ceremony at Israel's international airport. "France will maintain all its measures and sanctions until we are certain that Iran has renounced nuclear weapons."
Iran's suspect nuclear program will be high on the agenda of Hollande's visit. France is a member of the six global powers conducting negotiations with Iran.
Israeli Prime Minister Benjamin Netanyahu has been outspoken in his opposition to a potential deal in which the international community would ease some sanctions on Iran in exchange for some curbs on Iran's nuclear program. The countries fear that Iran is trying to build a nuclear weapon, a charge Iran denies.
Netanyahu's strong objections have raised tensions with the US, which said his concerns are premature. US officials, seeking to calm concerns in Israel and among its allies in Congress, say Iran will get only minor relief from the painful sanctions under the international proposal.
Hollande, accompanied by his girlfriend Valerie Trierweiler, was welcomed by an honor guard at Ben-Gurion International Airport near Tel Aviv.
"Israel sees in France a true friend," Netanyahu said at the ceremony, thanking Hollande for his positions on Iran.
"Iran must not be armed with nuclear weapons," Netanyahu said. "This wouldn't just endanger Israel and the countries in the Middle East but it would also endanger France, Europe and the entire world."
Speaking in Hebrew, Hollande said: "I will always remain a friend of Israel."
Israel views a nuclear-armed Iran as a threat to its very existence, citing Iran's repeated calls for the destruction of the Jewish state, Tehran's long-range missile program and its support for violent anti-Israel groups like the Hezbollah in Lebanon. Iran says its nuclear program is for peaceful purposes.
Netanyahu has repeatedly called the potential agreement between the six powers — the US, Russia, Britain, France, China and Germany — and Iran a "bad deal." He says international pressure should be increased, not eased, to pressure Iran into dismantling what he says is a military nuclear program.
"I hope we will be able to convince our friends this week ... to reach a much better deal, and it's possible to obtain that because Iran is under economic pressure and by the continuation of this pressure — and even by increasing it — can lead to a much better result of a diplomatic solution in peaceful ways," Netanyahu told his Cabinet ahead of Hollande's arrival.
Netanyahu said the Iran talks would dominate discussions with Hollande, as well as meetings with Russian President Vladimir Putin in Moscow on Wednesday. US Secretary of State John Kerry is scheduled to visit Jerusalem on Friday.
Israeli President Shimon Peres, in a speech welcoming Hollande at the airport, applauded the French president's "unflinching stance to prevent Iran from acquiring a nuclear weapon."
"Iran seeks to dominate the Middle East with nuclear arms and long range missiles. We stand, together, against this attempt which hangs as a dark shadow over the skies of the Middle East. In fact over the skies of the entire world," Peres said.
Both Netanyahu and Hollande said this week's meetings would also discuss the peace talks between Israel and the Palestinians. Since their launch in late July, the US-brokered negotiations have run into trouble, and both sides have said no progress has been made. Hollande is to meet Palestinian President Mahmoud Abbas later in the West Bank during his visit.
Netanyahu tried to play down his differences with US President Barack Obama, saying that disagreements happen even between the "best of friends" and that it is his government's duty to protect its interests.