President Barack Obama speaks to reporters following a National Security Council meeting on the Islamic State issue at the Pentagon in Washington on Monday.

AFP/Washington

US President Barack Obama voiced renewed determination to destroy the Islamic State group on Monday, vowing to win back territory in the Middle East and kill the group's leaders.

Sounding a notably more strident tone, Obama said that the US and its allies were taking the fight to Islamic State in Iraq and Syria.

"We are hitting them harder than ever," said Obama, in a second address following a seemingly IS-influenced attack in San Bernardino that has raised questions about his strategy.

"As we squeeze its heart, we will make it harder for ISIS to pump the propaganda to the rest of the world," Obama insisted at the Pentagon after meeting with US military leaders.

Listing a series of Islamic State leaders killed in coalition operations, Obama issued a stern warning.

"ISIL leaders cannot hide," he said. "Our next message to them is simple, you are next."

Even before the attack by a Muslim husband and wife in California killed 14 people, polls showed that more than 60% of Americans disapproved of the way Obama is handling the Islamic State and the broader terror threat.

As was the case in his primetime Oval Office address a week ago, Obama offered no shift in policy, but admitted: "We are recognising that progress needs to keep coming faster."