President Donald Trump defended his decision to withdraw all US ground troops from Syria within 30-days with a video in which he suggested it was a decision that dead US troops would have agreed with.

"And that's the way we want it, and that's the way they want it," Trump said, pointing a finger at the sky.

Trump took pride in his initial decision to continue combat operations in Syria during his presidency, but said he thinks it's time for that to end, citing his claims that the US has defeated ISIS.

Trump's decision caught Republican and Democratic lawmakers by surprise.

President Donald Trump defended his decision to withdraw all US ground troops from Syria within 30 days with a video in which he suggested it was a decision that dead US troops would have agreed with.

In a roughly one-minute video at the White House on Wednesday, Trump took pride in his initial decision to continue combat operations in Syria during his presidency, but said he thinks it's time for that to end, citing his claims that the US has defeated ISIS.

"We've been fighting for a long time in Syria," Trump said. "I've been president for almost two years and we've really stepped it up. And we have won against ISIS."

"We've beaten them, and we've beaten them badly," Trump added. "We've taken back the land and now it's time for our troops to come back home."

Trump's claim that the US had eradicated ISIS was undercut by an earlier claim from the US envoy to the coalition against the terror group.

"The military mission is the enduring defeat of ISIS," envoy Brett McGurk said, eight days before Trump's announcement.

"We have obviously learned a lot of lessons in the past, so we know that once the physical space is defeated, we can't just pick up and leave. So we're prepared to make sure that we do all we can to ensure this is enduring."

President Donald Trump gestures as he speaks to Navy and shipyard personnel aboard nuclear aircraft carrier Gerald R. Ford at Newport News Shipbuilding in Newport News, Virginia, March 2, 2017. AP Photo / Steve Helber

Trump expressed sympathy for US troops killed in Syria and said writing condolence letters to survivors "saddened" him. As of March, three US troops were killed in Syria.

"I get very saddened when I have to write letters or call parents or wives or husbands of soldiers who have been killed fighting for our country," Trump said. "It's a great honor. We cherish them. But it's heartbreaking. There's no question about it. It's heartbreaking. "

"Now we've won. It's time to come back," Trump added. "They're getting ready, you're going to see them soon. These are great American heroes. These are great heroes of the world because they fought for us but they've killed ISIS, who hurts the world. And we're proud to have done it."

Read more: Trump declares victory over ISIS as the US prepares to pull all troops out of Syria

Trump went on to speak for the dead troops by suggesting his decision was one they would have advocated.

"And I'll tell you, they're up there looking down on us, and there is nobody happier or more proud of their families, to put them in a position where they've done such good for so many people," Trump said. "So our boys, our young women, our men, they're all coming back. And they're coming back now. We won."

"And that's the way we want it, and that's the way they want it," Trump added, pointing a finger at the sky.

Roughly 2,000 US troops are now positioned to withdraw from Syria, where they have been conducting operations against ISIS and training Kurdish-led Syrian Democratic Forces since 2014.

US Marines firing a howitzer in Syria. US Marine Corps

Trump's decision caught Republican and Democratic lawmakers by surprise.

"If Obama had done this, we would be going nuts right now," Republican Sen. Lindsey Graham of South Carolina said.

Republican Sen. Ben Sasse of Nebraska also blasted the decision and described it as a hypocritical.

"Eight days ago the Administration called a hypothetical pullout 'reckless,'" Sasse said in a statement. "Today, we're leaving."

"The President's generals have no idea where this weak decision came from," Sasse said, adding that, "a lot of American allies will be slaughtered if this retreat is implemented."

While his authority to launch Tomahawk missiles against the Syrian regime for using chemical weapons was contested earlier this year, Trump's role as commander-in-chief to withdraw US forces leaves little room for a debate.

In remarks given to reporters on Wednesday, a senior administration official downplayed the abruptness of Trump's decision and suggested it was one that should not have come as a surprise.

"I will say the President's statements on this topic has been 100% consistent from the campaign through his announcement today," the official said. "And so the notion that anyone within the administration was caught unaware, I would challenge that, quite frankly. And it was the President's decision to make, and he made it."