Fresh violence in Syria has left nearly 30 people dead, days before a troop withdrawal is due to be implemented.
Opposition activists say at least 27 soldiers, rebels and civilians have been killed in violence in the past 24 hours.
The deaths come despite Syrian President Bashar al Assad agreeing to a peace plan devised by former United Nations Secretary-General Kofi Annan.
The envoy is trying to end more than a year of violence in which Mr Assad's forces have sought to crush pro-democracy demonstrations across Syria.
The Free Syrian Army has confirmed its fighters will stop shooting if Mr Assad withdraws his tanks and troops to barracks before a ceasefire deadline next Thursday.
The plan calls for a troop withdrawal by 10 April and a ceasefire two days later.
Mr Assad has said he accepts the terms.
But on Saturday, UN Secretary-General Ban Ki-moon sharply criticized the Syrian government for the persistent attacks on civilians and demanded it keep its pledge to halt all military operations.
Refugees fleeing from Syria into Turkey say Syrian army activity is intensifying, with the pressing of a new military offensive, the ABC reports.
Satellite images published
The United States has released satellite images it says show Syria has artillery poised to hit residential areas and has moved some forces between towns despite the withdrawal agreement.
The release on Facebook is part of an effort to pressure Mr Assad to pull back forces.
The terms of Mr Annan's peace plan include Syria immediately ceasing troop movements towards population centres and ending the use of heavy weapons in such areas.
It also calls for Syria to begin pulling back military concentrations in and around population centres.
While the United States says Syrian forces have indeed withdrawn from some areas, the US ambassdor to Syria Robert Ford cites media reports that they have fired artillery at residential areas in several towns over the last two days and have carried out "arrest sweeps" in Damascus suburbs.
"This is not the reduction in offensive Syrian government security operations that all agree must be the first step for the Annan initiative to succeed," said Mr Ford in a message on Facebook.
"The regime and the Syrian people should know that we are watching," he said.