'Circumstances' where US combat troops could be deployed against IS - Obama US president Barack Obama has said there might be circumstances where US troops are deployed in a combat role in the battle to defeat the Islamic State terrorist group, but declined to outline what they would be. Addressing the media at the end of the G20 summit in Brisbane on Sunday, Mr Obama also denied that the US was actively planning to oust Syrian dictator Bashar al-Assad, although he foreshadowed there would come a time when Syrians and regional powers would have to have a discussion about the country's political future. "Yes, there are always circumstances in which the United States might need to deploy US ground troops," Mr Obama said, before outlining a hypothetical and, at least now, far-fetched scenario. If we discover that ISIL has got possession of a nuclear weapon and we have to run an operation to get it out of its hands ... I would order it. Mr Obama said there could be other instances where the US could deploy troop against the Islamic State terrorist group, also known as IS or ISIL. So the question ends up being what are those circumstances. I'm not going to speculate on those. The US, like Australia, has been adamant it would only send troops to Iraq to train and advise local forces. Mr Obama announced recently that the number of US military advisers will be doubled to 3000. Australia has deployed 200 special forces personnel to train Iraqi forces. Western nations have refrained from supporting the mission to degrade and destroy IS with combat troops for fearing of stoking local resentment of an invasion of Muslim lands. Asked to respond to reports the US was now developing a strategy to topple Mr Assad, Mr Obama flatly denied the suggestion. We are looking for a political solution eventually within Syria that is inclusive of all the groups that are there - the Alawite, the Sunnis, Christians. At some point, the people of Syria and the various players involved, as well as regional players - Turkey, Iran, Assad's patrons like Russia - are going to have to engage in a political conversation ... But we are not even close to being at that stage. As for his discussions at the G20 with Russian President Vladimir Putin, Mr Obama described them as "business-like and blunt" We will maintain the economic isolation while maintaining the possibility of a diplomatic solution. It's not our preference for Russia to be isolated," he said. At this point, the sanctions we have in place are biting plenty good. We have our teams constantly looking at mechanisms in which to turn up additional pressure as is necessary.