Israel's army said Tuesday Damascus has used chemical weapons, as Pentagon chief Chuck Hagel wrapped up a visit to the Jewish state as part of a Mideast trip dominated by the Syrian war.

A senior officer in Israel's military intelligence alleged the Syrian regime had resorted to chemical weapons as Hagel met with Israeli Prime Minister Benjamin Netanyahu shortly before departing for Jordan and Saudi Arabia.

But US Secretary of State John Kerry said later that Netanyahu had been unable to confirm to him that the regime of Syrian President Bashar al-Assad had used chemical weapons.

"To the best of our professional understanding, the (Assad) regime has made use of deadly chemical weapons against the rebels in a number of incidents in the last few months," said Brigadier General Itai Brun, head of the research and analysis division of military intelligence.

Speaking to delegates at a Tel Aviv security conference, he cited an incident on March 19 in Aleppo province in which 31 people were killed, pointing to the physical symptoms suffered by those in the area at the time.

"The reduced pupils, the foam coming out of the mouth and other additional signs provide evidence that deadly chemical weapons have been used," he said, indicating the symptoms were observed in photographs.

"Which chemical weapons? Apparently sarin. The regime is also using chemical weapons that neutralise and are not fatal," he added.

Sarin is a deadly and volatile nerve agent that is colourless and odourless.

The United States has said any use of chemical agents would cross a "red line," evoking possible military action.

Britain and France, in documents presented to the UN, also suspect Syria has used chemical weapons but Washington said it is still reviewing intelligence accounts.

"The United States continues to assess reports of chemical weapons in Syria," Hagel's spokesman George Little said in a statement.

But he warned the Assad regime against the use of chemical agents or allowing them to fall into the hands of groups like Lebanon's Hezbollah.

"We reiterate in the strongest possible terms the obligations of the Syrian regime to safeguard its chemical weapons stockpiles, and not to use or transfer such weapons to terrorist groups like Hezbollah," he said in Jordan.

Kerry said he had telephoned Netanyahu following reports of their use.

"I think it is fair to say (the prime minister) was not in a position to confirm that in the conversation... I do not know yet what the facts are," said the US secretary of state.

The war in Syria and the possible use of chemical agents topped the agenda in Hagel's talks with Jordan's Prince Faisal and army chief General Masbal al-Zaben, officials said.

Hagel has bolstered an American military contingent in Jordan to more than 200 troops to help prepare for worst-case scenarios, including securing chemical weapons sites in Syria or a spillover of violence from the conflict.

After his brief stopover in Jordan, the US defence secretary headed to Riyadh and also planned to visit Cairo and Abu Dhabi this week.

Hagel is using the trip to put the finishing touches on a $10 billion dollar arms deal that will see the sale of advanced US missiles, radar and aircraft to Israel, missiles for warplanes to Saudi Arabia and F-16 fighter jets to the United Arab Emirates.

US officials see the arms package as sending a warning signal to Iran, which Washington accuses of propping up the Syrian regime and secretly developing a nuclear arsenal. Iran insists its nuclear programme is purely for peaceful purposes.

In Riyadh, Hagel planned to hold talks Tuesday evening with the defence minister and crown prince, Salman bin Abdulaziz al Saud.

Hagel had been originally scheduled to meet Prince Khaled bin Sultan bin Abdulaziz, the former powerful deputy defence minister. But he was sacked by a royal decree just days before Hagel's arrival, in an unusual move.

He was replaced by Prince Fahd bin Abdullah bin Mohammed, who commanded Saudi naval forces since 2002.

The move was the latest in a reshuffle of princes holding government posts in the oil-rich kingdom amid concerns about the monarch's age and frequent hospitalisation.

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