As Syria faces charges it may have supplied Hezbollah with Scud missiles, experts say spotting the weapons is no easy task -- which US and British forces learned in the first Gulf war.

Smuggling missiles and mobile launchers into Lebanon without US or Israeli intelligence agencies noticing would be "possible, but difficult," one US defense official, who spoke on condition of anonymity, told AFP.

Missiles and mobile launchers could be taken apart to avoid detection, analysts said.

"All you have to do is separate the tail from the missile, which is something you can do easily. And then move it to some other vehicle," said Anthony Cordesman of the Center for Strategic and International Studies, a Washington think tank.

Israel has accused Syria of arming Hezbollah with the ballistic missiles, a charge Damascus vehemently denies. US officials meanwhile say they cannot confirm if the weapons have been delivered to the Lebanese Shiite militia.

In the 1990-91 Gulf war, allied aircraft -- along with US and British special forces on the ground -- struggled to track and take out Saddam Hussein's mobile Scuds, which were hidden in gullies and culverts and quickly shifted out of sight after any launch.

"We flew thousands of missions to try to destroy Saddam's Scuds which he was firing at Israel and Saudi Arabia. After the war we discovered we had missed every single time," said Bruce Riedel, a former CIA officer and fellow at the Brookings Institution.

Sensors and other military technology have improved since then, and Lebanon offers a smaller area to monitor than Iraq.

Moreover, Israel has "very good intelligence there," Riedel said, "so they would probably do better."

Once inside Lebanon, the missiles and launchers could be reassembled and hidden until Hezbollah was ready to use them.

"The missiles are most vulnerable when they are preparing to launch. Still it would be difficult to destroy every launcher before they fired," he said.

Scud-type missiles, originally designed and produced by the Soviets, are usually about 11 meters (yards) long and have a range of roughly 300 kilometers (186 miles), though some versions can strike beyond 500 kilometers.

Adding Scuds to Hezbollah's arsenal of rockets would strengthen the militia's position even though Israel would retain its military edge, analysts said.

"It does not dramatically change the equation but it means Hezbollah can fire at any target in Israel," Cordesman said.

A much bigger concern for Israel would be if the Scuds came with chemical warheads, experts said, but no one has made that allegation so far.

Whether or not Scuds have been delivered, the Obama administration is convinced that Syria is stepping up military support to Hezbollah, US officials said.

"There's a narrow question of Scuds but there is a much broader concern about advanced weaponry," a US official, who asked not to be named, told reporters.

"The cooperation between Syria and Hezbollah is escalating and we think that is potentially destabilizing and adds risks in a region that already has more risks than it knows what to do with."

It remained unclear why the accusation against Syria was leveled by the Israeli president, Shimon Peres, and not by military or intelligence officials who usually present such charges along with more details, analysts said.

Some lawmakers in the US Congress have seized on the allegations to argue against Washington's efforts to promote dialogue with Syria.

President Barack Obama in February appointed Robert Ford as the first US ambassador to Damascus in five years, although the Senate has yet to confirm him.

US Secretary of State Hillary Clinton said Thursday in Estonia that "as of today" the United States sought to pursue deeper ties with Syria, suggesting Obama's policy could change if Damascus was found to be sending missiles.

Opting to supply Hezbollah with more powerful weaponry would fit in with a recent pattern in which Syria appears to have adopted a "triumphalist mindset," wrote Steven Heydemann at the US Institute of Peace.

US and European diplomacy has failed so far to persuade Syria to move away from Iran's orbit and forge stronger ties to the West, he wrote on the Foreign Policy website.

"Instead, Syria's leaders have pocketed their gains and raised the stakes, strengthening Hezbollah's arsenal and deepening its strategic ties with Iran," Heydemann wrote.