Activists said a car bomb near a key military airport in Damascus has killed 10 Syrian soldiers and wounded 10 others.
The Britain-based Syrian Observatory for Human Rights said the bomb Monday targeted a checkpoint near the Mazzeh military airport in an upscale neighborhood in western Damascus.
The violence comes as Russia - which has a veto in the U.N. Security Council - said it will not permit no-fly zones to be imposed over Syria.
Foreign Ministry spokesman Alexander Lukashevich made the comments Monday before planned talks between President Vladimir Putin and U.S. President Barack Obama on the sidelines of the G8 summit in Northern Ireland.
Russia and the United States are trying to bring representatives of Syrian President Bashar al-Assad and his foes to the negotiating table, but Moscow has criticized U.S. plans to arm rebel forces and to consider imposing a no-fly zone.
The United States said last week it has obtained proof that Syria used chemical weapons and will now send direct military aid to the rebels. Washington has not specified what that aid will be. Russia has been sending weapons to the Syrian government but says it is only fulfilling contracts.
Meanwhile, Mr. Assad denied U.S., British and French claims that his forces had used chemical weapons against his people during the escalating Syrian conflict.
According to an interview to appear in Tuesday's edition of the Frankfurter Allgemeine Zeitung newspaper, he also warned that European powers would "pay the price" if they sent weapons to rebel forces seeking to topple him.
The Syrian president said arming anti-government rebels would lead to terrorism in Europe.
Also Monday, the Palestinian Islamist Hamas movement issued an unusual criticism of the Lebanese Hezbollah militia, calling on the Shi'ite group to withdraw its forces from Syria and focus on fighting Israel instead.
Hamas, which controls the Gaza Strip, was once an Assad ally but last year endorsed the revolt against him.
The United Nations says the civil war in Syria has killed about 93,000 people over the last two years. Most of those killed have been civilians.