Washington: The US and Israel are closely monitoring Syria's suspected cache of weapons of mass destruction, fearing that terror groups could take advantage of the revolt against President Bashar al-Assad to seize chemical weapons and long range missiles.

US intelligence services believe Syria's non-conventional weapons programmes include significant stockpiles of mustard gas, VX and Sarin gas and the missile and artillery systems to deliver them.

"We are very concerned about the status of Syria's WMD, including chemical weapons," Israel's ambassador to the US Michael Oren said in an interview, the Wall Street Journal reported.

"Together with the US administration, we are watching this situation very carefully," he said.

The Washington and Tel Aviv are also concerned with worries that North Korea may have provided Syria with Nuclear related equipment.

The concerns come in the wake of UN investigators recently concluding that Damascus had been secretly constructing a nuclear reactor with North Korean help before Israeli jets destroyed the site in late 2007.

Israel has historically held concerns about the fall of the Assad regime, which has largely kept the Syria-Israel border quiet for the past 40 years. Still, Prime Minister Benjamin Netanyahu's government has increasingly voiced support for democratic change in Damascus.

"We see a lot of opportunity emerging from the end of the Assad regime," Oren said.

A senior US official said Syria's suspected chemical weapons arsenal "is of great importance and...under intense study."

US and Israeli officials won't disclose exactly how they are keeping tabs on Syrian weaponry. But in the past, the US and Israel have tracked activities at Syrian military installations using satellites and human spies.

In 2008, the George W Bush administration released detailed photographs and other intelligence of a reactor allegedly set to produce weapons-grade plutonium on the Euphrates River in eastern Syria.

Washington's concerns about Syria mirror in some ways those held about Libya, where US intelligence agencies are trying to help rebels secure mustard gas, shoulder-fired missiles and light arms amassed by Muammar Gaddafi's regime in recent decades. The Obama administration is concerned these weapons could fall into the hands of militant groups and terrorist organizations operating across North Africa and the Middle East.

Assad's government has repeatedly denied that it has developed any nuclear, chemical or biological weapons. It accuses Israel of having developed the largest nuclear and chemical weapons arsenal in the Middle East, a charge Israel neither confirms nor denies.

Syria is one of six nations that isn't a signatory to the Chemical Weapons Convention, which bans the production and stockpiling of chemical weapons.