The Syrian navy shelled two densely populated residential districts of the main Mediterranean port city of Latakia on Sunday.
"I can see the silhouettes of two grey vessels. They are firing their guns and the impact is landing on al-Raml al-Filistini and al-Shaab neighborhoods," one witness told Reuters by phone from Latakia, where tanks and armoured vehicles deployed three months ago to crush dissent against President Bashar Assad.
Tank fire killed at least eight people in Latakia on Sunday, residents said, bringing the total killed since the beginning of the assault on Saturday to 10. The Syrian Observatory for Human Rights said nine civilians were killed and 25 wounded on Sunday.
Assad is from Syria's minority Alawite sect. Latakia is majority Sunni with a large Alawite population, encouraged by the state to move there with offers of cheap land and jobs.
Demonstrations against Assad during the five-month uprising against his autocratic rule have been biggest in Sunni neighborhoods of Latakia, including Salibiya in the center of the city and Raml al-Filistini and al-Shaab on the southern shore.
Troops and tanks have been besieging the two neighborhoods for months, residents say, with garbage going uncollected and electricity regularly being cut.
The use of naval artillery -- generally seen as an escalation on Assad's part -- comes as Saudi Arabia and its Gulf allies have taken the lead from the Obama administration and recalled its ambassadors demanding an immediate halt to the violence in Syria.
The United States, which has yet to recall its ambassador to Syria, usually considered a pro-forma move when strong diplomatic disapprobation must be shown, has yet to impose sweeping sanctions on the Syrian regime -- instead targeting specific individuals -- or call for Assad's ouster.
Last week U.S. ambassador to Syria Robert Ford said he believed the "power and reputation" of the United States was sufficient to send Assad the message it was time for the bloodshed to stop.
"First of all, there is just the power, the reputation of the United States," Ford told ABC. "When I visited Hama, that was a statement and it got international attention that the American ambassador would go there. That’s leverage."
"In addition, because we have targeted specific individuals and worked with partners, especially in Europe, we are seeing some of those individuals and other people who fear being named on sanctions lists coming to us and saying maybe I need to rethink what I have been doing," Ford added.
Thus far Assad seems blithely unconcerned with the reputation or power of a United States unwilling to take broad material action to stop his regimes ongoing bloody crackdown on pro-reform protesters in the country.
Elswhere, at least 16 protesters were reported killed by Assad gunmen in Deir Al Zour on Saturday.
Rights observers say some 2,000 civilians have been killed by Assad gunmen to date.