Amid continued rocket fire into Israel, which has expanded to the center of the country and put nearly 4 million Israelis at risk, Washington continued to stand by Jerusalem as Operation Pillar of Defense entered its fifth day on Sunday.

During a telephone conversation with Prime Minister Benjamin Netanyahu over the weekend, U.S. President Barack Obama stressed that Israel "has the right to defend itself."

Netanyahu expressed appreciation to Obama and the American people for U.S. investment in the Iron Dome rocket and mortar defense system, which is being used to defend Israel against rocket attacks from Gaza, saving many Israeli lives, the White House said.

Obama reiterated U.S. support for Israel's right to self-defense and discussed possible ways to scale back the conflict, the White House said. It did not offer specifics.

Other officials in the Obama administration, however, have expressed hesitation over Israeli actions in Gaza, calling on Jerusalem to avoid launching a ground operation in the Hamas-ruled territory.

Obama also expressed regret for the loss of Israeli and Palestinian civilian lives.

On Saturday, the White House reiterated that it believed Israel “has the right to defend itself” against attack and that the Israelis would make their own decisions about their “military tactics and operations.”

A top aide to Obama told reporters traveling with the U.S. president to Asia on Air Force One that the U.S. and Israel both wanted an end to the rocket fire from Gaza.

Defense Minister Ehud Barak called U.S. Defense Secretary Leon Panetta on Friday as Panetta flew from Bangkok to San Francisco after an Asia-Pacific tour, a senior Pentagon official said. In their second phone conversation this week, Barak briefed Panetta on the situation and the prospects for scaling back the violence.

Terrorist groups have staged rocket attacks against Israel, which has responded by assassinating the military chief of the ruling Hamas militant group and conducting dozens of airstrikes on suspected rocket-launching sites and other Hamas targets in Gaza. In all, 27 Palestinians and three Israelis have been killed.

As part of continuous dialogue between Jerusalem and Washington during the recent round of fighting, U.S. Secretary of State Hillary Clinton spoke with Foreign Minister Avigdor Lieberman on Saturday, while National Security Council head Yaakov Amidror gives daily briefings to his U.S. counterpart Tom Donilon.

The U.S. Congress also continued to express unconditional support for Israel's position. On Thursday, the Senate unanimously passed a resolution, sponsored by 62 senators, stating that "Israel has the right to act in self-defense to protect the security of its citizens from terrorism." On Friday, the House of Representatives joined the Senate and unanimously passed a similar resolution.

French Foreign Minister Laurent Fabius was expected to visit Israel on Sunday for a meeting with political leaders in Jerusalem and Ramallah.

Ahead of his visit, Fabius apparently engaged in some shuttle diplomacy with Egypt in an attempt reach a cease-fire between Israel and Hamas. The efforts come before a visit by U.N. Secretary-General Ban Ki-moon to Israel scheduled for next Tuesday.

Meanwhile, leaders around the world have echoed U.S. support for Israel, but some have also conveyed reservations about a possible Israeli ground operation in Gaza.

German Chancellor Angela Merkel said on Friday that Egypt should exert its influence over Hamas to calm the situation in the Gaza Strip. A spokesman for Merkel noted that the chancellor was monitoring the situation with "great concern" and said that she believed that "Hamas is responsible for the outbreak of violence. There is no justification for firing rockets at Israel, which causes great suffering to the Israeli population."

Britain's Foreign Secretary William Hague released a statement on Saturday saying, "Hamas bears principal responsibility for the current crisis. I utterly condemn rocket attacks from Gaza into southern Israel by Hamas and other armed groups. This creates an intolerable situation for Israeli civilians in southern Israel, who have the right to live without fear of attack from Gaza. The rocket attacks also risk worsening the plight of Palestinian civilians in Gaza, which is already precarious. Hamas and other armed groups in Gaza should cease attacks against Israel immediately. I call on those in the region with influence over Hamas to use that influence to bring about an end to the attacks."

The British foreign secretary said he had spoken with Foreign Minister Avigdor Lieberman and emphasized that Israel also had a responsibility to calm tensions by acting according to international law and avoiding casualties among the civilian population in Gaza.

On Friday, he warned Israel about launching a ground mission, telling BBC Radio, "Israel does have to bear in mind that it is when ground invasions have taken place in previous conflicts that they have lost international support and a great deal of sympathy around the world."

"The thing that would bring this most quickly to an end would be for Hamas to stop launching rockets at Israel,” Hague said. “But of course, there are also responsibilities on Israel."