A bomb attack in December which killed 32 people took place after a ceasefire deal that paved the way for the government to take over the last rebel-controlled area of the city, which was a center of the 2011 uprising against President Bashar al-Assad.
Observatory director Rami Abdulrahman said the attack was the second most deadly of its kind in Homs since 2011, and the deadliest for almost a year and a half.
Violence rages on unabated across the country as world powers and the United Nations push to end the conflict, meeting in Geneva to try to broker a ceasefire.
Peace talks were suspended almost immediately earlier this month as Syrian government forces and their allies, backed by Russian air strikes, intensified assaults against insurgents in Aleppo province.
The latest fighting in the north of the country has displaced tens of thousands of people, many of whom headed for the Turkish border. The exodus added to more than 11 million already displaced by the conflict that has claimed 250,000 lives.