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.
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.