In a press conference with his Italian counterpart Sergio Mattarella, Donald Trump also denied giving Turkey the 'green light' to invade Syria.
US President Donald Trump denied on Wednesday that he had given Turkish President Recep Tayyip Erdogan a "green light" to launch operations against Kurdish militants in Syria.
"President Erdogan's decision didn't surprise me because he's wanted to do that for a long time," Mr Trump told reporters.
"He's been building up troops on the border with Syria for a long time.
"I didn't give him a green light," Mr Trump added. "Just the opposite of a green light."
"And I say: 'Why are we protecting Syria’s land?' Assad’s not a friend of ours. Why are we protecting their land?' And Syria also has a relationship with the Kurds, who by the way, are no angels," the US president continued.
Mr Trump also accused the Kurdistan Workers' Party, or PKK, of being "worse at terror and more of a terrorist threat, in many ways" than the Islamic State.
The remarks come as a senior US administration official insisted Mr Trump's pullout from Syria will not change his hard line on Iran, a key ally of President Bashar al-Assad.
In a Senate hearing, Mr Trump's Democratic rivals said he had strengthened adversaries by pulling US troops who had permitted de facto autonomy in northeastern Syria by Kurdish fighters, a force that led the battle to crush Islamic State extremists.
Faced with a Turkish incursion, the Kurds asked Assad's regime to return to the northeast of the war-battered country for the first time in years, with Russia patrolling in hopes of keeping the two sides apart.
"Withdrawing troops in northern Syria and greenlighting Turkey's brutal incursion gives new life to ISIS and hands over the keys to our national security to (Russian President Vladimir) Putin, Iran, and Assad," said Bob Menendez, the top Democrat on the Senate Foreign Relations Committee.
Brian Hook, the US special representative on Iran, replied: "The president's decision with respect to Syria is not going to change our Iran strategy or the efficacy of it."
"Our forces in northeast Syria have never had an Iran mission-set," he said.
But administration officials, notably former national security advisor John Bolton, had cited the Iranian presence in Syria as a reason to maintain US forces.
The administration has also warned that it will not contribute to the reconstruction of the war-battered country so long as Iranian troops are present.
Iran is an arch-foe for the Trump administration, which pulled out of a multinational deal on curbing Tehran's nuclear program and instead slapped punishing sanctions.
Iran, led by Shiite clerics, counts on Assad, a secular leader from the heterodox Alawite community, as its main ally in the Arab world.
On Monday, another senior official, speaking on condition of anonymity, said Turkey's incursion had upended US objectives including "the containment and expulsion of Iran."