France said on Tuesday the United Nations Security Council had to respond over the use of chemical weapons in Syria with a resolution that would punish those responsible for repeated attacks.

Syrian government forces used chemical weapons in opposition-controlled parts of Aleppo during battles to retake the city late last year, Human Rights Watch (HRW) said in a report published on Monday.

The findings add to mounting evidence of the use of banned chemical weapons in the six-year-old Syrian civil war and could strengthen calls by Britain, France and the United States for sanctions against Syrian officials.

While not confirming the report, a French foreign ministry spokesman said in a daily briefing the allegations were "extremely serious."

"It is up to the Security Council to act. France ... continues to discuss with its partners at the Security Council to adopt a resolution to punish those responsible for these attacks," the spokesman said.

"The use of weapons of mass destruction constitute a war crime and a threat to peace. Impunity is not an option."