At least 27 people were killed and over 60 injured near the Syrian capital of Damascus in attacks by pro-government forces on Tuesday, Al Jazeera reported. The attacks, which were allegedly carried out using improvised weapons known as “elephant rockets,” reportedly targeted rebel-held areas in the city of Douma, about 6 miles from Damascus.

These weapons are made by attaching rocket motors to much larger bombs -- a process that increases their destructive power while greatly reducing accuracy.

In the past, the Syrian regime has faced accusations of using chemical weapons and chlorine-filled barrel bombs on rebel forces and civilians in rebel-controlled territories. The Bashar Assad-led government, however, has consistently denied the allegations and blamed “terror groups” in the country for the use of such weapons.

Also on Tuesday, U.S. Secretary of State John Kerry said that the Syrian government’s use of chlorine gas had been “significantly documented.”

“I am absolutely certain -- we are certain -- that the preponderance of those attacks have been carried out by the regime. … That is not to say that some element of an opposition may not have had access [to chlorine gas] at one point in time or another, and have actually utilized something at one point in time or another,” Kerry said in a press briefing.

Earlier, in a report released in January, the Organization for Prohibition of Chemical Weapons (OPCW) concluded “with a high degree of confidence” that chlorine gas was used against civilians in Syria last year, killing at least 13 people. Although the international chemical weapons watchdog did not mention the offending party, Samantha Power, the U.S. ambassador to the United Nations, alleged at the time that the latest report provided more “compelling eyewitness evidence of chlorine gas use by Syria regime.”                 

In September 2013, the Syrian government agreed to declare and destroy its stockpile of chemical weapons. However, it did not have to declare its stockpile of the disinfectant chlorine because it is not recognized as a chemical weapon under international conventions.