VENEZUELAN President Nicolas Maduro has demanded an official investigation into leading opposition politician David Smolansky for falsely accusing the government of carrying out Syria-like chemical attacks against protesters.

Caracas-area mayor Mr Smolansky had attacked the use of a previously unseen red gas used to scatter thousands of anti-government protesters on Saturday.

The composition of the gas or smoke remains unclear but some protesters claimed that its use alongside volleys of tear gas produced nausea and vomiting.