■ Trump says withdrawal from Syria should come as 'no surprise'

■ Officials say decision will also put end to air campaign against ISIS

■ Putin says he doesn't understand pullout, but 'U.S. presence in Syria illegitimate'

■ Netanyahu vows to continue Israeli self-defense actions in region

■ Kurdish allies express sense of betrayal

U.S. President Donald Trump spoke out on Thursday in the wake of his administration's sudden announcement that it has decided to pull American troops out of Syria.

Taking to Twitter, the American president posed a question: "Does the USA want to be the Policeman of the Middle East, getting NOTHING but spending precious lives and trillions of dollars protecting others who, in almost all cases, do not appreciate what we are doing? Do we want to be there forever? Time for others to finally fight..."

Trump also tweeted that the decision to withdraw from the war-torn country "was no surprise."

Trump went on to explain the move, writing: "I've been campaigning on it for years," the U.S. president continued, "and six months ago, when I very publicly wanted to do it, I agreed to stay longer. Russia, Iran, Syria & others are the local enemy of ISIS. We were doing there work. Time to come home & rebuild. #MAGA"

He also addressed criticism of the decision, writing: "Russia, Iran, Syria & many others are not happy about the U.S. leaving, despite what the Fake News says, because now they will have to fight ISIS and others, who they hate, without us. I am building by far the most powerful military in the world. ISIS hits us they are doomed!"

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U.S. official told Reuters later on Thursday that Trump's order to withdraw U.S. troops from Syria also signifies an end to the U.S. air campaign against Islamic State there.

The U.S.-led air war has been critical to rolling back Islamic State and keeping pressure on the militant group in Iraq and Syria, with more than 100,000 bombs and missiles fired at targets in the two countries since 2015, according to Air Force data.

Some U.S. lawmakers were also critical of the move, reiterating claims it would serve as a win for ISIS, Iran and Russia.

Senator Lindsey Graham called the withdrawal "an Obama-like mistake" that "would be a big win for ISIS, Iran, Bashar al Assad of Syria, and Russia. I fear it will lead to devastating consequences for our nation, the region, and throughout the world."

Earlier Thursday, Russian President Vladimir Putin said that while he agreed with Trump that Islamic State had mostly been defeated, he did not understand what the American withdrawal from Syria meant because he has not seen signs of it yet.

The Russian president warned that there is a risk that ISIS militants would regroup, and called U.S. military presence in Syria illegitimate.

Meanwhile, Israeli Prime Minister Benjamin Netanyahu said that Israel will continue to defend itself "against Iran's attempt to entrench itself in Syria," noting that Israel doesn't intend to reduce efforts to curb Iranian aggression and to destroy terror tunnels on the Israel-Lebanon border.

Netanyahu said that he is aware that Israeli actions are being carried out "with the full support and backing of the U.S."

Washington's Kurdish partners warned that the move will allow Islamic State to regroup at a critical stage in the conflict, echoing alarm expressed by Western allies.

The U.S.-backed Syrian Democratic Forces (SDF) said Trump's withdrawal of all U.S. troops would also leave Syrians stuck between "the claws of hostile parties" fighting for territory in the seven-year-old war.

Trump's announcement on Wednesday upended a central pillar of American policy in the Middle East and stunned U.S. lawmakers and allies, who challenged the president's claim of victory.