The Local Coordination Committees group, which organises anti-regime protests on the ground, put the day's death toll at 19.
The latest violence comes after pro-democracy activists called for a "day of anger" on Tuesday in protest at Russia's backing for President Bashar al-Assad, whose regime has waged a deadly six-month crackdown on protesters.
"Do not support the killers. Do not kill the Syrians with your position" in favour of the regime, activists urged Russia in a posting on The Syrian Revolution 2011, a Facebook page that has been the engine for the revolt.
They wrote that a "day of anger" against Russia would be held on Tuesday.
"We express our anger towards Russia and the Russian government. The regime will disappear, but the people will live," the posting said.
Russia has blocked attempts at the United Nations to sanction Assad's regime and is promoting a separate draft resolution that simply calls on the government and the opposition to open direct talks.
Russian President Dmitry Medvedev on Monday defended the Syrian regime against sanctions for its crackdown, and also warned visiting British Prime Minister David Cameron of the dangers of such a move.
Cameron met Medvedev in Moscow for talks focusing on Syria and bilateral disputes as global frustration mounted with Russia's continued support for its ally.
A visiting Assad aide said 1,400 people -- half of them Syrian security and army forces -- had died in violence since the demonstrations erupted in mid-March.
However, UN High Commissioner for Human Rights Navi Pillay says 2,600 people have been killed in the crackdown.
The president of the UN Human Rights Council has appointed three experts to examine human rights violations in Syria, as mandated during an August emergency session.
A Council source said it would take "at least a month" before investigators go to Syria.
Nations such as France have accused Assad's regime of committing crimes against humanity and the foreign ministry in Paris said on Monday the UN Security Council's inability to approve a resolution on Syria was "a scandal."
But Medvedev refused to give any ground on what is fast becoming a heated sequel to the two sides' war of words over the NATO-led campaign in Libya.
He insisted the Kremlin was ready to put more pressure on Assad and argued his differences with the West were "not dramatic."
Yet he also stressed any punitive actions must be applied equally to both sides because the opposition was continuing to reject calls to engage in direct talks.
"This resolution must be strict, but it must not lead to the automatic application of sanctions," Medvedev said in reference to action proposed by Western powers.
Medvedev's push for dialogue was undermined by an Assad adviser in Moscow who appeared to reject the idea of establishing contacts with the opposition.
"Is there any party in Syria with which (Russia) could mediate?" asked Assad media adviser Bouthaina Shaaban. "There is no such party."
Her comments were followed hours later by Syrian dissident spokeswoman Basma Qadmani's announcement the opposition would on Thursday present a list of candidates for a "national council" similar to one formed in Libya.
Medvedev's tough talk and lack of progress on the ground left Cameron to acknowledge the two sides had essentially failed to bridge their gap on Syria.
"There is a difference of perspective between Russia and Britain on this issue," Cameron said. "Clearly, Britain would like to go further. We do not see a future for Assad."
Cameron also conceded a UN resolution may have to be abandoned in favour of a "clear statement about what is happening in Syria."
Britain and France have been leading the diplomatic offensive against Assad, and Paris issued another barb at what it called some nations' indifference to the bloodshed.
"How long will the international community remain blind and dumb in the face of this endless sequence of crimes? That's the question we're asking today," said French foreign ministry spokeswoman Bernard Valero.
The UN resolution Russia is blocking would most likely affect arms sales -- the one area left untouched by the powerful economic sanctions imposed already by the European Union and the United States.
Switzerland followed suit on Monday by widening its travel and financial embargo against Assad's regime to 19 individuals and eight institutions.
But Russia has been keen to preserve some $4 billion in current and future Syrian arms contracts and has taken more assertive steps in trying to persuade Assad to adopt political improvements that could keep his hold on power.
His aide Shaaban said after talks with the upper house of parliament's foreign affairs chief Mikhail Margelov that Syria favoured the cautious reform process seen in Russia since the Soviet Union's collapse.
"In the past 20 years, Russia has undergone various processes that led to structural changes," she said.
"We want things in Syria to develop the way they did in Russia, in a bloodless manner."
Margelov said he had received Assad's approval to send a group of Russian senators to Damascus and other Syrian cities to independently report on the situation on the ground.