US Defense Secretary Chuck Hagel on Tuesday promised Israel to be "clear-eyed" and committed to ensuring that Iran does not develop nuclear weapons as Washington pursues engagement.

Israeli Defense Minister Moshe Yaalon, whose government has pressed for a hard line, visited Washington a week before Iran meets six nations to ease international concerns on its nuclear program that have triggered a US-led campaign of sanctions.

"Secretary Hagel noted that while the United States intends to test the prospect for a diplomatic solution with Iran we remain clear-eyed about the challenges ahead," Pentagon spokesman George Little said.

The United States "will not waver from our firm policy to prevent Iran from obtaining nuclear weapons," he said.

Iran's newly elected President Hassan Rouhani, a self-styled moderate, sought to ease longstanding tensions with the West during a week-long visit to the United States, culminating in an unprecedented telephone call with US President Barack Obama on September 27.

Iran's US-educated foreign minister, Mohammad Javad Zarif, has said he hopes to reach a settlement over Tehran's nuclear program within a year and will present a package during October 15-16 talks in Geneva with the United States and five other powers -- Britain, China, France, Germany and Russia.

Iran says that its uranium enrichment work is for peaceful purposes. But Western powers and Israel, which is believed to have a clandestine nuclear program, charge that the Islamic republic is seeking an atomic bomb.

Israeli Prime Minister Benjamin Netanyahu has urged no let-up in pressure on Iran and not ruled out a military strike.

Hagel, a former Republican senator and Vietnam veteran turned opponent of the Iraq war, has tried to reassure Israel after facing stiff opposition to his nomination following his remark that a "Jewish lobby" was intimidating lawmakers in Washington.