Tony Blair says pressure on President Bashar al-Assad must be stepped up, calling events in Syria "appalling".
The former UK prime minister, who is now Middle East envoy, said leaving Syria alone would have "very brutal" and "very bloody" consequences.
He told the BBC many of the problems around Syria were about "what happened next" if Mr Assad were removed.
The new UN-Arab League mediator Lakhdar Brahimi warned on Sunday the crisis presented a "threat to the world".
After his first meeting with President Assad, he said: "The crisis is dangerous and getting worse, and it is a threat to the Syrian people, the region and the world."
Mr Blair, who is envoy for the Quartet - the UN, US, EU and Russia - was asked on BBC Radio 4's Today programme whether he would be advocating military action.
"I would be advocating ramping up where we are. How you do that, whether it is along the lines of what the Turks have suggested, creating zones of immunity, these are questions that we should debate," he said.
Source and full story: BBC News, 17 Sept 2012