The United States considered "half measures" unsatisfactory, White House spokesman Scott McClellan said in response to the redeployment of Syrian forces in Lebanon.
"This does not add up to Syria leaving Lebanon. Nobody has said all troops are leaving Lebanon," a State Department official said.
"We will continue to hold their feet to the fire, not accept half-measures and call a spade a spade - that is, when they make these announcements about a withdrawal that is neither complete or immediate, we will call it for what it is,” the official said.
Britain welcomes move as 'first step'
Meanwhile, Germany, France and Britain urged Syria to move swiftly.
"We expect Syria to withdraw its troops and security services completely and as quickly as possible," German Chancellor Gerhard Schroeder and French President Jacques Chirac said in a joint statement.
British Foreign Secretary Jack Straw said separately that Syria's move was welcome as a "first step", but added that Britain expects to see rapid progress to the withdrawal of Syrian troops from the whole of Lebanon."
Earlier Monday, Syrian soldiers based in the Lebanese mountain towns of Hamana, Mdairij, Soufar and Aley were dismantling communications equipment or loading military gear and belongings onto army trucks, witnesses said.
Some trucks with equipment and a few dozen soldiers from several posts headed eastwards, while other troops reportedly stayed behind.
Assad, Lahoud meet
A Lebanese security source said the posts were pulling out their equipment to other posts closer to the border to enable them to move out quickly when the orders come later this week.
Syrian President Bashar Assad and his Lebanese counterpart Emile Lahoud met Monday and agreed on a Syrian troop withdrawal.
The Syrian troops will complete their move to eastern Lebanon by March 31, said a statement after the talks. The Syrian and Lebanese military will then decide how long the Syrians stay there.