Pentagon chief Chuck Hagel and his Israeli counterpart on Monday hailed a major arms deal as a sign of "ironclad" US support for the Jewish state after talks on Iran's nuclear drive and Syria's war.

The US defence secretary, who has been accused of being too critical of Israel, sought to convey a message of solidarity on his first visit to the region since he took office two months ago.

Speaking at a joint news conference with Defence Minister Moshe Yaalon in Tel Aviv, Hagel confirmed the two had agreed on a multi-billion dollar weapons deal that will see Israel receiving an impressive array of advanced US missiles and aircraft.

"Today we took another significant step in the US-Israel defence relationship," Hagel said, reiterating Washington's "ironclad pledge" to ensure Israel's military edge in a region rocked by turmoil.

"Minister Yaalon and I agreed that the United States will make available to Israel a set of advanced new military capabilities," including anti-radiation missiles, radars for fighter jets, KC-135 refuelling aircraft, and the V-22 Osprey, which the United States has not released to other countries, he said.

Yaalon admitted Israel had already "acted" to stop advanced weapons from falling into militant hands, in what was seen as implicit confirmation of Israeli involvement in a strike on an arms convoy inside Syria in January.

He said Israel had laid down three "very clear red lines" for the regime of Syrian President Bashar al-Assad, the first of which was "not to allow sophisticated weapons to be delivered or be taken by... Hezbollah or other rogue elements."

"When they crossed this red line, we acted," he said, in what was widely understood to be the January 30 strike which hit what a US official said were surface-to-air missiles near Damascus that Israel suspected were en route to Lebanese Shiite group Hezbollah.

The second red line was maintaining security along the Israeli-Syrian ceasefire line on the occupied Golan Heights, and the third was the transfer of chemical weapons into the hands of militants, which "has not been tested yet," Yaalon said.

European diplomats have alleged the Syrian regime used chemical weapons against rebels, and Hagel said Washington was investigating the accounts.

"Currently our intelligence agencies are assessing what happened and what did not happen," he said.

The White House has warned that use of chemical agents in the Syrian civil war would constitute a "game changer" but Hagel refused to be drawn on any possible US response.

"I'm not going to discuss contingency options," he said.

The US defence secretary said he had had "clear, direct conversations" with Yaalon that covered the threat posed by Iran's nuclear programme, which Washington and much of the West believe is a drive for a weapons capability, but which the Islamic republic denies.

At a meeting on Monday between Hagel and Shimon Peres, the Israeli president said "your visit sends a message that you're determined not to let Iran become nuclear.

"I have full trust in your position," he said, adding that diplomacy in dealing with Iran was "better but if diplomacy won't be enough then all options are on the table."

US-Israeli relations have been strained over how to address the Iranian threat but Hagel had insisted there was no major disagreement on the issue.

Before arriving in Israel on Sunday at the start of a six-day regional tour, Hagel had said the arms deal sent a "very clear signal" to Tehran that military action remains an option to stop it from obtaining nuclear weapons.

Israel, believed to be the Middle East's sole if undeclared nuclear power, has refused to rule out a pre-emptive military strike on Iran's nuclear facilities, and Hagel on Monday said that "every sovereign nation has a right to defend itself".

During the afternoon, the US defence chief took a helicopter tour over the Israeli-occupied Golan Heights after which he returned to Jerusalem for talks with President Peres.

"I spent two hours this morning with Mr. Ya'alon, touring the north in a helicopter," Hagel later said.

"And I had been in those areas in my many visits here. But I'd never seen it the way that the minister had it laid out for me, the north along the border. "And when you have that experience, as you know so well, it really does shape the kind of challenges and the kind of world that Israel's living with, and in a clear way.

On Tuesday morning, he will meet Prime Minister Benjamin Netanyahu before leaving for a brief stopover in Jordan, then on to Riyadh and Abu Dhabi, where he will wrap up details of the $10 billion arms deal that will also provide missiles to Saudi and US F-16 fighter jets to the UAE.

He will also visit Cairo.