US Secretary of State Hillary Clinton said Washington would use "all elements of its power" to prevent Iran going nuclear and was working in "close consultation" with Israel over how to do so.
And she said a resumption of talks between Israel and the Palestinians would only come about if the parties "do the hard work for peace."
Speaking to reporters at the end of a whirlwind 24-hour visit to Jerusalem, Clinton said that Iran not yet decided to curb its nuclear ambitions, and warned that Washington would stop at nothing to prevent it from getting a nuclear bomb.
"We will use all elements of American power to prevent Iran obtaining a nuclear weapon," she said in remarks which carried an implied threat of military action -- a course of action never ruled out by Washington.
Thanks to US efforts to rally the international community to tackle the Iranian nuclear threat, Tehran was "under greater pressure than ever before," Clinton said, indicating that the Obama administration was "pressing forward in close consultation with Israel."
"I think it is fair to say we are on the same page at this moment, trying to figure our way forward to have the maximum impact on affecting the decisions that Iran makes," Clinton said.
Clinton arrived in Israel late on Sunday at the tail end of a nine-nation tour, holding talks with top officials including Prime Minister Benjamin Netanyahu, President Shimon Peres, Defence Minister Ehud Barak and Foreign Minister Avigdor Lieberman.
Although Israel has warned a nuclear Iran would pose an existential threat to the Jewish state and has refused to rule out a military strike on its nuclear facilities, Peres expressed confidence in Washington's tough stance on Tehran.
"I think the coalition we have built, and the measures you have taken are beginning to have their impact... they are the right start," he told Clinton.
"We appreciate very much your position. We trust its depth and dedication and determination and we feel partners of this coalition."
The US diplomat also briefed the Israelis on her talks with Egypt's new Islamist President Mohamed Morsi and sought to reassure them that the new Cairo administration had reaffirmed support for the peace treaty which she said had "served as a backbone for regional stability for more than three decades."
There has been some concern in Israel that Morsi, who emerged out of the Islamist Muslim Brotherhood, might seek to renegotiate the treaty.
Clinton said: "The amount of work ahead of this Egyptian government would be daunting for the most experienced leaders. The economy is in desperate need of reform.
"The political system is a work in progress, a long way from being finalised. There are serious fissures within society that have to be addressed."
In talks with Peres, Clinton updated him on "the latest developments and the approaches of the new Egyptian leadership, and stressed the importance of strengthening the relations between Israel and Egypt," the president's office said.
The stalled peace process was also high on the agenda, with Clinton reportedly telling Israel that Palestinian president Mahmud Abbas and his prime minister Salam Fayyad were the best peace partners Israel could have, the website of Haaretz newspaper reported, quoting an Israeli official at the talks.
And she also reportedly pushed Israel to make gestures to strengthen the Palestinian leader, Israeli press reports said.
But ultimately, a return to peace talks would be dependent on "hard work" by the two parties, she told reporters at a late-night press conference.
"So our goal remains an independent Palestinian state living in peace and security alongside a secure Jewish democratic state of Israel."
"We remain focused on the resumption of direct negotiations since we believe that is the only route to a lasting stable peace. The international community can help ... we stand ready to do so, to help support an environment for talks but it's up to the parties to do the hard work for peace," she said.
"To those who say the timing isn't right, the other side has to move first, or the trust just isn't there, I say: peace won't wait and the responsibility falls on all of us to keep pressing forward."
She also met with Fayyad in Jerusalem, describing their meeting as "excellent" and saying the Palestinian premier had briefed her on "the challenges that the Palestinian Authority faces and what the United States can do to support them."
Ahead of his dinner meeting with Clinton, Netanyahu thanked her for helping shore up Israel's ties with Egypt and said he was keen to hear about her talks with President Morsi in Cairo.
He also said the two would discuss ways to break the deadlock in peace talks with the Palestinians.
Direct peace talks between Israel and the Palestinians have been frozen for nearly two years following an intractable dispute over Jewish settlement building.
The Jerusalem visit came at the end of a 13-day tour of nine countries, with Clinton departing for Washington on a flight which took off shortly after midnight.