Syrian activists say a car bomb killed 18 people Wednesday in northern Syria.
The London-based Syrian Observatory for Human Rights says the blast in Idlib province targeted Syrian soldiers.
The new United Nations-Arab League envoy for Syria, Lakhdar Brahimi, heads to Damascus Thursday for a meeting with Syrian President Bashar al-Assad. Brahimi says his task in Syria will be difficult that he will try his best to give as much help as possible to the Syrian people.
The U.N. and Arab League have made no progress on reaching a cease-fire in Syria and starting talks on a transitional government.
European Union foreign policy chief Catherine Ashton says the world is deadlocked over Syria, warning of more radicalization and violence.
Ashton told the European Parliament that there is a dangerous stalemate in Syria. She says the opposition is fragmented and that there is no real alternative to the Assad regime.
Meanwhile, Syrian troops and rebels clashed in the commercial capital, Aleppo, near the city's government-held airport, as battles intensify ahead of a visit by the new international peace envoy to Syria.
The Syrian Observatory for Human Rights
and other activist groups said the heavy fighting erupted at dawn Wednesday in the Nayrab area, about five kilometers from Aleppo International Airport.
Timeline of the Uprising in Syria:
March 2011: First protests erupt, dozens killed. Government announces reforms, then resigns.
April, May 2011: Protests intensify and spread, hundreds killed. U.S. imposes sanctions on top leaders.
August, September 2011: Saudi Arabia, Kuwait and Bahrain withdraw ambassadors. U.S. imposes economic sanctions, EU bans Syrian oil imports.
October 2011: Russia, China veto a U.N. resolution condemning Syria.
November 2011: The Arab League suspends Syria's membership.
January 2012: Government releases 5,000 prisoners. Death toll soars past 7,000.
February 2012: Russia, China veto a second U.N. resolution condemning crackdown
March 2012: Former U.N. chief Kofi Annan holds talks in Syria. U.N. says death toll exceeds 9,000. Syria agrees to U.N.-backed peace plan.
April 2012: Syria says it will abide by a cease-fire on April 12, but violence continues. U.N. observers arrive.
May 2012: Syria holds parliamentary elections, violence continues, U.N.-Arab League envoy Kofi Annan appeals to Syrian President Bashar al-Assad to stop the violence.
June 2012: Western nations expel Syrian diplomats, Annan urges increased pressure on Syria.
July 2012: Red Cross expands areas of Syria it says are in civil war. Violence increases across the country.
August 2012: A day after Syrian warplanes attacked the rebel-controlled northern town of Azaz and a bombing near the U.N. observer headquarters in Damascus, the United Nations Security Council decided to end the U.N. monitoring mission in Syria when its mandate expires on August 19.
September 2012: Fighting intensifies in Aleppo and continues across the country. New U.N.-Arab League envoy, Lakhdar Brahimi, is expected to visit the country and meet with Assad.
The facility, which includes a military base, is widely used by the government to bomb rebel-held areas. Over the past several weeks, rebels have been attacking military airfields in an attempt to prevent them from being used for launching air strikes, while commercial facilities have been left alone.
Diplomatic efforts have so far failed to stop the bloodshed in Syria, but the new U.N.-Arab League envoy, Lakhdar Brahimi, plans to travel to the country this week in a bid to revive them.
U.N. Secretary-General Ban Ki-moon said Brahimi will sit down with President Bashar al-Assad when he makes his first official visit to Syria, although the date has not been set.
Brahimi replaces former envoy Kofi Annan, who failed to reach a cease-fire in Syria and open talks on a transitional government.
U.N. officials say the fighting in Syria has killed about 20,000 people, nearly all of them civilians, and driven more than one million from their homes.
More than 250,000 Syrians have fled to Jordan, Iraq, Lebanon and Turkey. The U.N refugee agency calls the humanitarian problems caused by the war its biggest crisis.