"We have been clear, and the (US) President has outlined, that his strategy entails not only broadening the effort against IS in Iraq and going on the offensive in support of Iraqi forces against IS in Iraq, but it will necessarily, in all likelihood, involve action in Syria, and he has said he is prepared to take that action," Rice said.
"I'm not going to give you any precision or prediction on when that might occur. Obviously we are working every day to build the coalition, that we're making good progress in that regard. There are other elements of the comprehensive approach that we're pulling together that are important aspects of the overall strategy," she said.
"We're focusing on multiple lines of effort, including using our unique military capabilities to deny IS safe haven and building the international coalition to support our efforts," she said.
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"Our strategy does not involve US troops on the ground in a combat role in either Iraq or Syria, and no US troops will be in Syria as part of the train-and-equip programme. This programme will be hosted outside of Syria in partnership with neighboring countries," Rice told White House reporters.
To date, more than 40 countries have offered assistance.
Rice said it would be a unified international coalition.
"I don't think we're going to have a bifurcated coalition. This will be a unified coalition. It's one operation. It'll be under a common command. We will continue to welcome the involvement of partners who will make different contributions, based on their capacity, based on their varying political circumstances," she said.
"It will be unified, it will be cohesive, and it will be under one single command authority," Rice the US National Security Advisor said in response to a question.