US President Barack Obama said he will explain to Americans and congressional leaders this week his plan to "start going on some offense" against Islamic State militants, who he said could eventually become a threat to the US. Obama will make a speech on Wednesday to "describe what our game plan's going to be," and meet congressional leaders on Tuesday to seek their support for his strategy to halt the militant Islamist group, which controls parts of Syria and Iraq."I just want the American people to understand the nature of the threat and how we're going to deal with it and to have confidence that we'll be able to deal with it," Obama said in an interview with NBC's "Meet the Press" that aired on Sunday. "The next phase is now to start going on some offense," he said, adding, "I want everybody to understand that we have not seen any immediate intelligence about threats to the homeland" from the Islamic State group, Obama said.But the group has attracted foreign fighters from Western nations who could travel to the United States "unimpeded," Obama said. "Over time, that can be a serious threat to the homeland."