Western spy agencies suspect the Syrian government has dispersed several hundred tons of chemical weapons and precursor components across as many as 20 sites across the country, The Washington Post reported on Thursday.

The sites are being monitored, but officials told The Washington Post there is growing fear that the monitors have not identified every location and that some of the poisons could be stolen or used by Syrian troops against civilians.

“We think we know everything, but we felt the same way about Libya,” said a former U.S. intelligence official who has been briefed on U.S. preparations for both conflicts. “We had been on the ground in Libya, yet there were big surprises, both in terms of quantities and locations.”

The former official was one of several people who spoke to The Washington Post on condition of anonymity to discuss classified information.

The collapse of government control in several Syrian provinces has prompted heightened scrutiny of the weapons depots by the United States and its allies in the region. It also has hastened preparations for securing the sites with foreign troops, the officials said.

Drawing from recent intelligence assessments, U.S. and Middle Eastern officials believe the Syrian arsenal contains several hundred tons of chemical weapons and precursors, including sizeable quantities of battlefield-ready sarin, the deadly nerve agent.

The stockpile appears to be larger and more scattered than originally believed, two officials who have seen the intelligence reports told the newspaper. They said the most dangerous chemical stocks are kept in bunkers in about a half-dozen locations, while as many as 14 other facilities are used to store or manufacture components.

Because of the risks posed by the stockpile, U.S. intelligence agencies have devoted enormous resources to monitoring the facilities while they devise plans to safeguard them if the crisis worsens, current and former U.S. officials said.

“It’s obvious that ensuring their security is paramount,” a U.S. official told The Washington Post. “Planning for different scenarios, consulting appropriately with allies and preparing to manage any new challenges is simply being responsible.”

Several current and former officials acknowledged the extreme difficulty of securing chemical depots inside Syria with fighting underway and the likelihood of fierce resistance from Syrian forces to any incursions by outsiders. Some of the officials also conceded that yet-undetected facilities could exist within a country roughly the size of Washington state.

The terrorism risk has prompted extensive contingency planning by the United States and regional allies, including Israel, Jordan and Turkey, U.S. and Middle Eastern officials told the newspaper.

Under the most optimistic scenario, teams of weapons experts could be dispatched into rebel-controlled parts of Syria to secure and remove chemicals, as happened in. However, if weapons sites are overrun during fighting — or if loyalist forces are seen preparing for a chemical attack — plans call for dispatching elite military forces to secure the weapons under fire, if necessary, according to U.S. and Middle Eastern officials briefed on the preparations.

Israel has expressed concerns that Assad’s chemical weapons will end up in the hands of the Hizbullah terror group if his regime falls.

Syria has admitted it has chemical weapons and has threatened to use them if attacked by external forces. It claimed it will not use these weapons on rebels fighting to oust Assad.

Recent reports from Syria indicated that Assad has transferred a battery of advanced missiles to the al-Masna border crossing, which is the central route used to transfer equipment and weapons to Hizbullah. Members of the Syrian opposition said that one of two major chemical arsenals of the Syrian regime is located near that border crossing.

This facility is located just 24 kilometers from a missile base belonging to Hizbullah and was first exposed by the London Times newspaper in May of 2010.

French President Francois Holllande recently warned that any use of chemical weapons by Syria would be sufficient reason for Western countries to intervene in Syria.

Hollande said that France was working along with several other countries to create a protective zone around Syria, to be in position to move in if necessary.

A similar warning was also made a week earlier by U.S. President Barack Obama, who said that President Bashar al-Assad should heed U.S. warnings to neither use nor move chemical or biological weapons.

“We cannot have a situation where chemical or biological weapons are falling into the hands of the wrong people,” Obama told reporters at the White House. “We have been very clear to the Assad regime — but also to other players on the ground — that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized.”

He added, “That would change my calculus; that would change my equation.”