Prime Minister Lee Hsien Loong has laid out Singapore's position on the use of chemical weapons in Syria, saying that the perpetrators must be punished.

Speaking to the Singapore media in Russia on Friday at close of the G20 summit, he said that while it is still unclear who is behind the attacks, action needs to be taken once it is established.

He added, however, that any response should come under the auspices of the United Nations, even though this was not always possible. Even then, he said some other ways might need to be found to "punish the perpetrators in a way that is consistent with international law".

He said that Singapore had considered carefully its position on such weapons, noting that the small country would have a "severe problem" if such weapons were deployed.