WASHINGTON • United States President Barack Obama has vowed to continue hammering Islamic State in Iraq and Syria (ISIS) targets in Iraq and Syria, but acknowledged that pressure on the militants was prompting them to lash out beyond their self-proclaimed caliphate.

He also blasted President Vladimir Putin's policy in Syria, saying he doubted the Russian leader could be trusted to cooperate in helping to end the country's bloody civil war.

Speaking after a briefing on Thursday from his top national security advisers on the expanding war against ISIS in Iraq, Syria and most recently Libya, where US planes have been bombing in support of a government offensive near Sirte, Mr Obama pledged the militant group would "inevitably" be crushed and said the US-led coalition would continue to aggressively target the militants "across every front".

"As we've seen, it is still very difficult to detect and prevent lone actors or small cells of terrorists who are determined to kill the innocent and are willing to die," Mr Obama said. "And that's why... we're going to keep going after ISIL aggressively across every front of this campaign," he said. ISIL is another acronym for ISIS.

He pointed to a string of battlefield defeats suffered by ISIS in the past year as proof that the group is "not invincible", and said US- backed Iraqi forces would use a recently recaptured air base as a hub to take back Mosul, ISIS' largest stronghold in Iraq.

Mr Obama said he was confident that ISIS would continue to lose territory as Iraqi and Syrian forces, backed by American air power, close in on Mosul, Raqqa and strongholds near the Turkish border.

"ISIL has not been able to reclaim any significant territory that they have lost," he said. "I want to repeat, ISIL has not had a major successful offensive operation in either Syria or Iraq in a full year. Even ISIL's leaders know they're going to keep losing."

But "the decline of ISIL in Syria and Iraq appears to be causing it to shift to tactics that we've seen before - an even greater emphasis on encouraging high-profile terrorist attacks, including in the United States". The greatest danger posed by the group is one of overreaction, Mr Obama added. "How we react to this is as important as the efforts we take to destroy ISIL. The reason it is called terrorism is that these are weak enemies that can't match us in conventional power, but what they can do is make us scared."

Even as coalition planes target ISIS areas in Iraq and Syria, the Russians have simultaneously been bombing in Syria to support President Bashar al-Assad.

While Moscow has sometimes struck ISIS targets, many of its strikes have been against anti-Assad rebels. Multiple rounds of international negotiations to end the war, which erupted in 2011 after the Assad regime unleashed a brutal crackdown against a pro-democracy revolt, have so far failed.

Mr Obama said the US was prepared to work with Russia to try to reduce the violence in Syria and boost the fight against ISIS and Al-Qaeda. "But Russia has failed to take the necessary steps. Given the deteriorating situation, it is time for Russia to show it is serious about pursuing these objectives," he said, warning he was not confident he could trust Mr Putin.

The militants swept across vast parts of northern Syria and Iraq in 2014, leaving a trail of human butchery and horrific destruction in their wake. Since then, the coalition has conducted daily plane and drone strikes - over 14,000 so far - and worked with local forces on the ground to gradually reclaim the seized territory.

WASHINGTON POST, AGENCE FRANCE-PRESSE