Jerusalem (CNN) -- The United States won't let Iran obtain a nuclear weapon, "period," but sanctions remain the best tool to keep Tehran off the nuclear path, Defense Secretary Leon Panetta said during a Wednesday visit to Israel.
Panetta said that united, international pressure was "the most effective way to stop Iran from obtaining a nuclear weapon."
"We have been steadily applying more and more pressure against Tehran, focusing on diplomatic and economic sanctions, and I believe these steps are having an effect," Panetta said after reviewing an Israeli missile-defense battery with Defense Minister Ehud Barak. But he said international leaders must keep "maximum pressure" on Iran, and he said the United States has "a full range of options -- including military options -- should diplomacy fail."
Panetta assured Israeli leaders that Washington, its leading ally, "stands firmly with Israel" and has a "rock-solid" commitment to is security. After talks with Prime Minister Benjamin Netanyahu, the Pentagon chief said the United States "will not allow Iran to develop a nuclear weapon, period."
But Netanyahu was more skeptical, saying, "Time to resolve this issue peacefully is running out."
"However forceful our statements, they have not convinced Iran that we are serious about stopping them," Netanyahu said. "Right now, the Iranian regime believes that the international community does not have the will to stop its nuclear program."
Iran has refused international demands to stop producing enriched uranium, insisting that its work is aimed at fueling civilian nuclear reactors. But many Western countries, particularly Israel, fear that the program is a cover for Iran to develop atomic weapons, and the International Atomic Energy Agency says it can no longer verify that the Iranian program is strictly peaceful.
U.S. spy agencies believe that Iran has not decided to pursue nuclear weapons but that it is building the "scientific, technical and industrial capacity" that would allow it to do so, James Clapper, the national intelligence chief, told a Senate committee in February. There are concerns that the window for a diplomatic solution to the problem may be closing, and a military strike by Israel -- the leading U.S. ally in the region -- against Iran's nuclear program may be on the horizon.
Israeli President Shimon Peres said last week that Iran was in an "open war" with Israel after he pointed the finger at Iran and Hezbollah for a bus bombing in Bulgaria last month that killed five Israelis.
The Obama administration announced new sanctions on Iran on Tuesday, targeting its petrochemical industries as well as banks in China and Iraq that U.S. officials say helped Iranian authorities evade existing sanctions. Iranian oil exports have been cut by 40%, the International Energy Agency reports. The rial, Iran's currency, has dropped by nearly the same amount, fueling rampant inflation and taking a steep toll on ordinary Iranians.
Panetta is on a weeklong trip to the Middle East and North Africa. His stop in Israel came three days after presumptive Republican presidential nominee Mitt Romney visited Jerusalem and pledged to support any measures to keep Iran from developing a nuclear bomb.
At the outset of his trip, Panetta said the issue "hasn't been easy." But, he added, "I think the fact is that when the United States, Israel and the international community remain unified in our position against Iran, that that's the best way to convince Iran to pull back from what they are doing and to abide by international rules and regulations."
Strong support for Israel is a core element of U.S. policy in the Middle East, and the two countries collaborate on military planning and research. One example of that was the "Iron Dome" anti-missile system he saw up close in Ashkelon, a project that received significant funding from the U.S. government.
Panetta's tour of the Middle East has already touched on a number of sensitive foreign policy issues in the region.
On Monday, he expressed confidence that President Bashar al-Assad of Syria will eventually be forced out of power by the bloody civil war raging in the country.
"I'm sure that deep down, Assad knows he's in trouble, and it's just matter of time before he has to go," Panetta said in Tunisia. "I would say if you want to be able to protect yourself and your family, you better get the hell out now."
And on Tuesday, he met with the first democratically elected president in Egypt's history, Mohammed Morsy, who is struggling to counterbalance the influence of the country's military rulers.
The powerful Supreme Council of the Armed Forces wields legislative power, having ordered the dissolution of parliament after the country's highest court ruled that it had been elected under invalid laws.
Morsy tried to call it back into session, but the court reaffirmed its decision, so the military council retains lawmaking powers until a new parliament is sworn in near the end of the year.
Panetta also met with Egypt's longtime top military leader, Field Marshal Muhammad Tantawi, who has played a key role in running the country since the fall of the strongman ruler Hosni Mubarak last year.
"Based on what I've seen and the discussions I've had ... President Morsy and Field Marshal Tantawi have a very good relationship and are working together towards the same end," Panetta said Tuesday.