Israeli claims Syrian President Bashar Assad's troops have used chemical weapons against rebel forces have intensified pressure on the United States to intervene in Syria's civil war.

U.S. President Barack Obama left himself exposed to such pressure when he declared during a visit to Israel in March that the use of chemical weapons, or their transfer to U.S.-designated terrorist groups, would be a "game-changer."

It was noticeable when U.S. Defense Secretary Chuck Hagel made his inaugural visit to Israel this week that the main topic of concern appeared to be the threat of Syria's chemical arsenal rather than Iran's nuclear program.

But the deepening concerns about Syria's sizeable chemical weapons arsenal has led to widening speculation the Americans and their allies are moving closer to military intervention in Syria.

This was heightened by the April 17 deployment of 200 U.S. troops from the 1st Armored Division to Jordan, Syria's southern neighbor where U.S. and British Special Forces are training Syrian rebel fighters.

Most of the troops being deployed are command and logistics experts, suggesting they would be need to organize combat force to intervene in the Syrian war which is threatening to destabilize an already turbulent Middle East.

The Los Angeles Times reported the troops would be the vanguard of a planned 20,000-strong U.S. force if the Obama administration decides to secure Syria's chemical weapons.

Hagel said the 1st Armored contingent wasn't intended to pave the way for large-scale intervention, but to "improve readiness and prepare for a number of scenarios."

He didn't elaborate but there were disturbing reports of a growing momentum by Israel toward intervention in Syria amid growing tension on the occupied Golan Heights, Israel's northern frontier with Syria.

France's Le Figaro newspaper reported Sunday that Jordan, which signed a peace treaty with Israel in 1994, has agreed to provide air corridors for Israeli drone aircraft to monitor Syrian territory.

Israel has long worried about Assad's chemical weapons falling into the hands of jihadist rebels, particularly the al-Nusra Front, the most formidable of the rebel factions which have made substantial advances against Assad's hard-pressed forces in recent weeks.

Israel also fears the Syrians may have also transferred chemical weapons, along with advanced surface-to-air and surface-to-surface missiles, to Hezbollah, its Lebanese ally which Damascus has used to maintain military pressure on the Jewish state for three decades.

Israeli concerns were substantially heightened Tuesday by Brig. Gen. Itai Brun, chief analyst of Israel's Military Intelligence, who accused the Syrian regime of repeatedly using chemical weapons, including the nerve gas sarin, against rebels in recent months.

That was the most categorical assertion by an Israeli leader on the chemical weapons issue to date.

Israel, it must be said, has a vested interest in encouraging the Americans and their allies to intervene to ensure that Assad is toppled and succeeded by a moderate regime from Syria's Sunni majority, not one dominated by jihadists linked to al-Qaida who have sworn to eradicate the Jewish state.

Intelligence sources in the region say the Obama administration has considerable doubts about Brun's claims but they do echo a recent assertion by Britain and France that Damascus has employed chemical weapons against the rebels.

On April 19, these two countries told the United Nations there was "credible evidence" that chemical weapons have been used several times since December.

Damascus has refused to allow U.N. investigators to inspect areas supposedly affected by such attacks but London and Paris have cited smuggled soil samples collected from alleged attack sites in Damascus and the war-torn cities of Homs and Aleppo further north, as well as witness interviews and credible rebel sources.

Given Israel's growing concerns, Western officials say there are worries that, if the Syrian jihadists did deploy chemical weapons, Israel would be provoked into taking unilateral action, much as it has threatened to take against Iran's nuclear program.

"We're very, very close to the red line," one British official told London's Guardian newspaper.