Israel's outgoing ambassador to the United Nations said Monday that the most significant threat to the Jewish state is not Iran, but efforts to delegitimize Israel and its leaders.

"Israel is the most isolated, lonely country in the world," Gabriela Shalev told reporters in Washington at a luncheon sponsored by the Israel project.

Ms. Shalev, who will leave her post on Aug. 31, said the "first challenge" Israel faced was the campaign to delegitimize the Jewish state, a campaign she said has taken the form of lawsuits brought against Israeli officials in European courts, and unfair attention paid to Israeli misdeeds within the U.N. and its various committees.

She said the other major challenges for Israel included the threat from Iran as both a potential nuclear power and a leading sponsor of terrorism, as well as the lack of a peace agreement with the Palestinians. But because from her perspective the international community is acting to pressure Iran with the latest sanctions resolution at the United Nations, the biggest threat to Israel now is the campaign to question Israel's right to exist and defend itself.

Susan E. Rice, U.S. ambassador to the United Nations, praised Ms. Shalev during a reception in New York last week and noted that being U.S. ambassador in the Turtle Bay neighborhood of Manhattan is not always easy, but that "being Israels ambassador to the United Nations is never easy."

Mrs. Rice said that the United States will continue to bolster Israel's "qualitative military advantage so that Israel can always defend itself, by itself, against any threat or possible combination of threats." Mrs. Rice's remarks were reported in Haaretz.com.

Diplomatically, Mrs. Rice said, the United States also will defend Israel. "We will continue U.S. efforts to combat all international attempts to challenge the legitimacy of Israel - including and especially at the United Nations," she said.

Since Israel in 2008 launched Operation Cast Lead against Hamas targets in Gaza, which involved F-16 strikes, Israel has faced particular scrutiny from within the United Nations.

Last year, the U.N. Human Rights Council released a report authored by a South African judge, Richard Goldstone, that was critical of Israel's conduct in the war.

In particular, the report said Israel deliberately targeted civilians, a claim that relied on testimony from Hamas.

Israel contends that Hamas deliberately placed military targets among the civilians and points out that citizens were sent text messages urging them to leave areas of the strip that would be bombarded.

After the Goldstone report, some Palestinian groups began bringing civil lawsuits against high Israeli officials for the conduct in the Gaza war in European courts.

Ms. Shalev, a well-known Israeli jurist and academic, said the new campaign of delegitimization was in the context of other Arab efforts to make war against Israel.

"They did not succeed in the wars, then the economic boycott failed, then the terrorism failed; now it is delegitimization," she said.

"I think this really depends on what delegitimization constitutes. If its criticizing the occupation, the wall or the settlements, then it is perfectly legitimate and totally fine. If it is broad-based calls for boycotts of Israel that question the legitimacy of Israel as a state, then it is delegitimization and it is problematic and counterproductive," said Hussein Ibish, a senior fellow at the American Task Force on Palestine.

Mr. Ibish added: "There is an unfortunate tendency in certain parts of Israeli discourse to conflate these phenomena that are distinct and should not be lumped together."

The ambassador said she had full confidence that the Obama administration would continue to give Israel diplomatic protection inside the United Nations.

But she also said that the Obama administration had made no specific promise to oppose a plan to launch an international investigation of Israel's handling of a Turkish aid flotilla in Gaza on May 31.

During that incident, Israeli commandos killed nine activists aboard the Mavi Marmara after being attacked with crude weapons as they descended from a helicopter.

The investigation is favored by U.N. Secretary-General, Ban Ki-moon and opposed by Israel.

However, Ms. Shalev said Israel "may abide" by Mr. Ban's plan for the investigation.