The bomb targeted a bus carrying day laborers in northwest Idlib province, the Syrian Observatory for Human Rights, based in London, told CNN.
U.N. Secretary-General Ban Ki-moon once again called on Syrian President Bashar Assad to "stop killing your own people."
Ban, speaking at a meeting on government reform and transition to democracy held in Beirut, Lebanon, said the lesson to be learned from the regime changes in the region during the past year, collectively called the Arab Spring, is clear -- the era of dictators and family dynasties is past.
"I say again to President Assad of Syria: Stop the violence. Stop killing your own people," Ban said. "The path of repression is a dead end."
Ban noted the revolutions that started in Tunisia and swept across Egypt, Libya and Yemen did not start with a call for a regime change.
"First and foremost," he said, "people wanted dignity. They want an end to corruption. They want a say in their future. They want jobs and justice -- a fair share of political power. They want their human rights.
"The old way, the old order, is crumbling -- one-man rule and the perpetuation of family dynasties; monopolies of wealth and power; the silencing of the media; the deprivation of fundamental freedoms that are the birthright of men, women and children on this planet."
Ban also pledged the United Nations' commitment to help Arab countries through their transition.
Various rights groups estimate at least 5,000 Syrians have been killed since anti-government protests began in March, the majority of them civilians.
The Arab League has a fact-finding contingent in Syria, scheduled to conclude Thursday.
Since the league became involved in recent weeks, Syria has released 5,000 political prisoners.
Assad announced a second political amnesty Sunday dating back to March 15, the state-run Syrian Arab News Agency reported.
Assad has repeatedly refused international calls to step down to end the bloodshed and allow for democratic reforms. Both Iran and Russia have shown support for his government.