A missile defense shield jointly developed by the United States and Israel is intercepting nearly 90 percent of Palestinian rockets that appear to be a threat to populated areas, Israel claimed Friday while making clear that it is not now seeking U.S. military help.

The conflict that began Wednesday is the largest test yet of the Iron Dome missile defense system designed to protect southern Israeli towns from rockets fired from the bordering Palestinian territory of Gaza. Its limits were evident Friday, when two Palestinian rockets were fired toward Jerusalem, beyond the zone regularly protected by Iron Dome.

Israel has called up thousands of reservists and massed troops at the Gaza border as fighting escalated Friday in what Israel’s ambassador to the United States called an armed conflict that could become a full-scale war. Speaking with reporters in Washington, Israeli Ambassador Michael Oren said Israel “will take any and all measures to protect our citizens.”

Oren did not rule out the possibility that Israel could appeal for U.S. assistance.

“Right now we have the military means at our disposal that we need to meet this threat, and we are not asking for anything beyond that,” Oren said. “But we are in constant consultation and communication with our American counterparts about the situation on the ground.”

In the 2006 Israeli invasion of Lebanon, Israel waited several days to request U.S.-made cluster munitions. The State Department later found that Israel had probably violated U.S. ground rules for the use of the controversial munitions in civilian areas.

While traveling in Singapore, Secretary of State Hillary Rodham Clinton spoke Friday with the Israeli foreign minister and made her second call in as many days to the Egyptian foreign minister, State Department spokeswoman Victoria Nuland said. The United States is urging Egypt to use its influence with Hamas to dial back the conflict. Clinton also spoke Friday with Jordan’s King Abdullah II.

“In all cases, her message has been the same — that we are urging a de-escalation of this conflict,” Nuland said.

Defense Secretary Leon E. Panetta, returning from an Asia trip, spoke by telephone with Israeli Defense Minister Ehud Barak on Friday. Defense officials said that it was the second call in recent days between the two leaders and that they discussed prospects for de-escalating the conflict in Gaza.

The advent of longer-range rockets could hasten an expanded Israeli response, including a ground invasion of Gaza. No rockets have hit Jerusalem in four decades, but Friday’s launches confirmed that militant groups have the capacity to fire munitions much deeper inside Israel.

Hamas, the militant group that controls Gaza, said it had developed the two “M-75” rockets that were fired toward Jerusalem on Friday. The rocket type, with a range of approximately 46 miles, had not been previously used by Hamas, although the group was known to have some longer-range rockets.

Hamas has also been amassing longer-range Iranian-built Fajr-5 rockets and appears to have used one in a fatal attack in Kiryat Malakhi on Thursday. The rocket also has a range of up to about 46 miles, posing a threat to half of Israel’s population.

Israeli officials would not specify the type of rocket that struck an apartment building in Kiryat Malakhi in southern Israel on Thursday, killing three people.

“When the [Gaza] operation was planned, we were very much aware of this capability, and we understood that this could happen,” a senior Defense Ministry official said. “We know Hamas has been gaining capability over time, but this is the first time we’ve seen it used.”

The Iranian rockets are larger than the ones Hamas has traditionally used. Western intelligence officials say components are smuggled into Gaza — most likely through tunnels across the Sinai border — and assembled in small factories disguised as residences.

“We don’t think they have that many more,” Oren said of the
longer-range rockets.

Israel’s air assault on rocket sites inside Gaza has been largely successful, Oren and other Israel officials claimed, and the longer-range rockets that have been launched in this conflict have caused no casualties.

“They haven’t caused any damage, they haven’t caused any casualties,” Oren said. “It’s more of a psychological issue so far.”

Israeli officials released updated figures Friday that they said show improving performance knocking down incoming rockets. By late in the day, Iron Dome batteries had destroyed 192 of the 200 Hamas rockets the system had sought to engage, Israel’s Ministry of Defense reported.

“Iron Dome continues to be an amazing success story, with a 90 percent success rate,” Oren said. “In terms of defending the south, it’s really a remarkable story.”

Israeli Prime Minister Benjamin Netanyahu, who called President Obama on Friday, expressed his “deep appreciation” for the U.S. investment in the Iron Dome defense system, the White House said in a statement.

The United States has invested heavily in the Iron Dome, with lawmakers approving an estimated $900 million spread over several years. Its advanced radar system calculates the flight path of incoming rockets and decides within seconds whether a rocket’s course will lead to a populated areaor empty field. More than 400 Hamas rockets were allowed to land because they were deemed to be of little threat, said a senior Israeli defense official,who spoke on the condition of anonymity to discuss the system’s performance.

“The result has actually been better than we expected,” the official said.

“Obviously, Hamas has made significant improvements to its arsenal,” mostly by smuggling in better equipment, said a Middle East weapons analyst, who spoke on the condition of anonymity to discuss confidential assessment of Hamas’s military capability.

Oren said Hamas’s arsenal also included Syrian rockets and Libyan weapons smuggled out of that country after the fall of dictator Moammar Gaddafi.

Warrick reported from Amman, Jordan. Karin Brulliard in Jerusalem and Craig Whitlock contributed to this report.