BEIRUT -- President Bashar Assad's forces killed at least 50 civilians, including 13 children, in central Syria on Friday, activists said. It was one of the highest death tolls in one specific area since an internationally-brokered cease-fire went into effect last month.

Syrian troops using tanks, mortars and heavy machine guns pounded the area of Houla, a region made up of several towns and villages in the province of Homs, the Britain-based Syrian Observatory for Human Rights and the Local Coordination Committees activist groups said. Both groups said at least 50 people were killed. The Observatory, which has a network of activists around the country, said the dead included 13 children. It added that about 100 people were wounded.

Homs has been among the hardest-hit provinces in a government crackdown since the uprising against Assad's regime began in March last year. The UN said several weeks ago that 9,000 people have been killed in Syria in the past 15 months.

Attacks like Friday's, as well as strikes by rebel forces on government troops, have persisted despite the deployment of more than 250 UN observers who have fanned out across Syria to monitor a cease-fire brokered by international envoy Kofi Annan.

In a report to the Security Council obtained by the AP on Friday, UN Secretary-General Ban Ki-moon says "unacceptable levels of violence and abuses" are taking place daily in Syria in violation of the peace plan, and he is putting much of the blame on the Syrian government. Ban said there has only been "small progress" on some measures, singling out the government's failure to halt attacks or stop using heavy weapons.

The deployment of UN military observers "appears to be having a calming effect," but Ban said "the overall level of violence in the country remains quite high."

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