The Syrian government is "in contravention" of an agreed peace plan by keeping troops and heavy weapons in cities, UN leader Ban Ki-moon said Thursday.
Ban also said he was "gravely alarmed" by reports of shelling of populated areas in Syria, in a statement released after the death of scores of people in the protest city of Hama.
The UN secretary general "remains deeply troubled by the continued presence of heavy weapons, military equipment and army personnel in population centers, as reported by United Nations Military Observers," said the statement released by UN deputy spokesman Eduardo del Buey.
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This is "in contravention of the Syrian government's commitments to withdraw its troops and heavy weapons from these areas."
Ban demanded that President Bashar al-Assad's government "comply with its commitments without delay."
Assad's government agreed the withdrawal with UN-Arab League envoy Kofi Annan as part of a six-point peace plan for Syria, where the UN says well over 9,000 people have died since an uprising started in March last year.
The fierce new condemnation of Assad came amid reports by activists that scores of people had been killed in shelling of a district of Hama by government forces. Two UN observers are based in the city.
Ban is "gravely alarmed by reports of continued violence and killing in Syria, including shelling and explosions in various residential areas as well as armed clashes," said the statement.
"He condemns in the strongest terms the continued repression against the Syrian civilian population and violence from any quarter. This situation is unacceptable and must stop immediately."
"The secretary general reminds all concerned parties, particularly the government of Syria, of the need to ensure that conditions for the effective operation of the United Nations Military Observers are put in place immediately, including a sustained cessation of armed violence."
The UN Security Council has approved a 300-strong military observer force to monitor a cessation of hostilities that started on April 12 but has barely held.
Western nations have expressed strong doubts that the observers will be able to work. The United States has already warned it may not renewed the mission's initial three month mandate.
