US Vice President Joe Biden said on Monday Washington was going to have to "squeeze the heart of" the Islamic State group (ISIS or IS) in Syria and Iraq to wipe it out.
"We have to squeeze the heart of Daesh in Iraq and Syria so they can't continue to pump the poison in the region and the rest of the world," he said, using an Arab acronym for ISIS.
Biden was speaking to hundreds of American and allied forces inside a hangar at a military base in the United Arab Emirates.
"This fight is going to take time, but we are committed to seeing it through until we wipe out this evil – and we will wipe out this evil," Biden said.
Earlier, he ruled out a military solution to end Syria's conflict, and called for a political transition.
"That should be clear to everyone," Biden told Abu Dhabi newspaper The National at the start of his visit to the UAE ahead of travelling to Israel and Jordan.
So as hard as it is, we have to keep trying to reach a political settlement," he said.
Saudi Arabia, which backs the Syrian opposition, and ally the UAE have said they are willing to send ground troops to Syria under US command to battle ISIS.
Biden's comments come as President Bashar al-Assad's regime and its opponents are due this week to resume UN-sponsored peace talks in Geneva as a fragile ceasefire holds in Syria.
The talks are aimed at ending the five-year Syria war that has killed more than 270,000 people, displaced millions and devastated the country.
Sticking point: Assad's fate
The fate of Assad, who is refusing to step down, has been one of the main sticking points in talks.
"A political solution between the parties is the only way to end the violence and give the Syrian people the chance they deserve to rebuild their country. To create a credible, inclusive, and non-sectarian system, a new constitution and free and fair elections," Biden said.
He said the truce that went into effect in Syria on February 27 "seems to be holding" but was "not perfect."
But he also noted that "levels of violence have dropped significantly across the country", and said this opened the way for the delivery of desperately needed humanitarian aid.
Biden also praised US relations with the UAE and its partners in the six-nation Gulf Cooperation Council, which also includes Saudi Arabia, Qatar, Kuwait, Bahrain and Oman.
He acknowledged the "challenges" posed by the historic nuclear deal struck last year between Iran and world powers and also the concerns it raised in GCC countries which are wary of Tehran.
"That's why we worked so hard to achieve a nuclear agreement with Iran, because as dangerous as Iran's actions are, they would be exponentially greater if Iran possessed a nuclear weapon."
He said steps were being taken to bolster the security of the GCC monarchies to be able to "deal with Iran diplomatically from a position of strength".
Biden was to hold talks later Monday with UAE President Sheikh Mohammed bin Zayed al-Nahyan and on Tuesday with Dubai ruler Sheikh Mohammed bin Rashid al-Maktoum.
AFP contributed to this report.