The death tolls were contradicting in various reports after the devastating bomb destroyed a restaurant and damaged cars and buildings near Al-Jala hospital in the centre of Benghazi, reported Agence France-Presse.
Protests were carried out across the streets, against the insecurity of the city which was the inception point of the uprising against late dictator Moamer Gadhafi.
Deputy Interior Minister Abdullah Massoud said 15 people were killed and 30 wounded in the attack. He stressed it was a preliminary toll.
Witnesses said children were among the casualties of what commentators said was the first attack of its kind to hit Libyan civilians in broad daylight since the 2011 uprising.
Dozens of people including, rushed to the scene, volunteering to gather body parts and place them in plastic bags, AFP journalists reported.
The bombing wrecked cars and scattered debris. The deputy interior minister said the blast "totally destroyed a restaurant" and damaged buildings near the hospital. A Benghazi security official said, "We don't know yet whether the attack targeted civilians or a particular individual."
"The members of the Security Council underlined the commitment of the international community to support Libya's successful transition to a secure, peaceful and prosperous democracy," added the statement released late Monday.
Benghazi, Libya's second city, has seen a wave of violence in recent weeks.
But previous attacks, bombings or assassinations, have rocked the city by night or in the early hours when the streets are empty, and have hit non-civilian targets.
Authorities blame radical Islamists for the violence being carried out in the recent times.
Obama said on Monday that the campaign, which hit new heights with House of Representatives hearings on the issue last week, "has been a sideshow", reports AFP.
Monday's car bombing comes three weeks after a similar attack on the French embassy in Tripoli.
France and Britain led the creation of a NATO no-fly zone in Libya in 2011 which played a key role in the overthrow of Gadhafi.