"The window for a diplomatic solution simply cannot by definition remain open forever, " he told a news conference.

BBC: John Kerry urges Syrian opposition to attend Rome talks

As he has said, the President believes that the window of opportunity for a diplomatic resolution to this matter will not remain open indefinitely, and he retains all options on the table for keeping that commitment to prevent Iran from acquiring a nuclear weapon.

WHITEHOUSE: Press Briefing

Asked if the window for such military action was "almost shut", he said, "the window is still open to try to work towards a diplomatic solution".

BBC: Obama steers cautiously on Iran