Although the government of President Bashar Assad has permitted few journalists into the country since rebellion began in January 2011, a report Sunday from the Syrian Observatory for Human Rights in London said there was "widespread mortar and heavy machine gunfire," Voice of America reported.
The group said in a release from London artillery shells were being fired into Homs at a rate of three per minute.
There was no report of fatalities or casualties, although the United Nations estimates at least 9,000 people have died as a result of the political upheaval since last year.
Meanwhile, the 15-member U.N. Security Council on Saturday unanimously authorized the deployment of 30 unarmed monitors to Syria, with an option to deploy as many as 200 more.
In Geneva, U.N. Secretary-General Ban Ki-moon said there would be a U.N. summit there April 20 to address how to deal with at least 1 million people displaced by the violence in Syria.