All options on table over Syria: Pence

US Vice President Mike Pence says 'all options are on the table' for the US response to the poison gas attack on citizens in Syria.

The US secretary of state says it's time for Russia to think carefully about its support for Syria. (AAP)

US Vice President Mike Pence says "all options are on the table" for a US response to a poison gas attack in Syria that Washington has blamed on Syria's government.

Pence also said in an interview with Fox News on Wednesday that Russia must fulfill its obligation under a 2013 agreement to eliminate chemical weapons from Syria.