The blasts, one from a car bomb and another from a suicide attack, struck the Zahra district in the middle of the city, said the observatory.
Sana, Syria’s state news agency, reported two car bomb blasts, but gave a lower initial toll of six dead and 37 wounded.
It was the second major attack in the city since a ceasefire deal took effect earlier this month, paving the way for the government to take over the last rebel-controlled area of Homs.
Twin blasts on December 12, also in Zahra, killed at least 16 people. Islamic State claimed responsibility for that attack, saying it had detonated a suicide car bomb.
Under the Homs ceasefire deal, at least 700 insurgent fighters and members of their families left the last rebel-controlled area of the city, al Waer district.
The UN presided over implementation of the deal.
Meanwhile, Iraqi forces backed by US-led airstrikes drove Islamic State militants out of the centre of Ramadi and seized the main government complex there, according to military officials, who said insurgents are still dug into pockets of the city west of Baghdad.
Ramadi, the provincial capital of the western Anbar province, fell to IS in May, marking a major setback for Iraqi forces and the US-led campaign.
In recent months Iraqi forces have launched several offensives to retake Ramadi, but all had stalled. Iraqi troops began advancing into some parts of the city earlier this month.
Heavy fighting and limited access to frontlines made it difficult to follow the troops’ progress, and Iraqi officials issued a string of sometimes contradictory statements.
Brigadier General Ahmed al-Belawi said IS militants stopped firing from inside the government complex at around 8am Monday and said troops were encircling it as engineering teams cleared booby traps.
A few hours later, military spokesman Brig Gen Yahya Rasool announced Ramadi had been “fully liberated”.
Gen Ismail al-Mahlawi, head of military operations in Anbar, clarified that Iraqi forces had only retaken the government complex and that parts of the city remained under IS control.
He said IS fighters still control 30% of Ramadi.