Republicans and now some Democrats have criticised Mr Obama's plans, seizing on his earlier statements that the militants had been "contained".
"We are going to continue the strategy that has the best chance of working," he told reporters in Turkey on Monday.
However, he said the US would intensify its efforts against the militants.
At times sounding frustrated, Mr Obama pushed back against those who say the US is not doing enough to stop IS.
"This is not a traditional military opponent. We can retake territory and as long as we keep our troops there we can hold it. But that does not solve the underlying problem of eliminating the dynamics that are producing these kinds of violent, extremist groups," Mr Obama said.
He called the attacks in Paris on Friday that killed at least 129 people "a terrible and sickening setback" in the fight against IS.
Mr Obama said most of differences among his political opponents on how to fight IS is about tone not tactics.
"Some of them seem to think that if I were just more bellicose in expressing what we are doing that that would make a difference, because that seems to be the only thing that they're doing, is talking as if they're tough," he said.
His more muted comments were in contrast to those of  French President Francois Hollande who said France is "at war".
Although most Republicans have opposed Mr Obama's IS policies, some fellow Democrats are breaking ranks to criticise the president.
"[IS] is not contained. [IS] is expanding," Democratic Senator Dianne Feinstein of California told the MSNBC news channel. "They've just put out a video saying it is their intent to attack this country,"
US President Barack Obama has defended his administration's strategy against the so-called Islamic State, rebuffing calls to send ground troops to Syria.