Turkey launched the cross-border assault on Kurdish fighters last Wednesday after Trump withdrew some US troops from the region, drawing sharp criticism from fellow Republicans who accused him of abandoning allies who had helped him fight against Islamic State of Iraq and the Levant (ISIL or ISIS) armed group.
Turkey says the offensive aims to remove the Kurdish-led Syrian Democratic Forces (SDF) from the border area and create a "safe zone" to which millions of Syrian refugees can be returned.
Ankara considers the Kurdish People's Protection Group (YPG), which forms the backbone of the SDF, a "terrorist" group linked to Kurdish separatists inside Turkey.
Trump said he would send Vice President Mike Pence and National Security Advisor Robert O'Brien to Ankara as soon as possible in an attempt to begin negotiations.
Pence said Trump had spoken directly to Turkey's president Recep Tayyip Erdogan, who promised not attack the border town of Kobane.
"President Trump communicated to him very clearly that the United States of America wants Turkey to stop the invasion, implement an immediate ceasefire and to begin to negotiate with Kurdish forces in Syria to bring an end to the violence," Pence said.
The sanctions apply to individuals, entities or associates of the Turkish government involved in "actions that endanger civilians or lead to the further deterioration of peace, security and stability in northeast Syria", US Secretary of State Mike Pompeo said in a statement.
In his sanctions announcement, Trump said he was halting negotiations on a $100bn trade deal with Turkey and raising steel tariffs back up to 50 percent. The president also imposed sanctions on three senior Turkish officials and Turkey's defence and energy ministries.
In a statement announcing the move, Trump said he was "fully prepared to swiftly destroy Turkey's economy if Turkish leaders continue down this dangerous and destructive path".
Trump said Turkey's military offensive was "endangering civilians and threatening peace, security and stability in the region".
According to the US Treasury, Turkish Minister of Defence Hulusi Akar, Interior Minister Suleyman Soylu, and Energy Minister Fatih Donmez were placed on the department's sanctions blacklist, freezing their assets in the United States and banning US or US-related transactions with them.
"I have been perfectly clear with Erdogan: Turkey's action is precipitating a humanitarian crisis and setting conditions for possible war crimes," Trump added in his statement.
"Turkey must ensure the safety of civilians, including religous and ethnic minorities, and is now, or may be in the future, responsible for the ongoing detention of ISIS terrorists in the region."
Treasury Secretary Steven Mnuchin said the sanctions would hurt an already weak Turkish economy and Pence warned the US would continue to ramp up the sanctions unless Turkey "was willing to embrace a ceasefire, come to the negotiating table and end the violence."
In an editorial published in Wall Street Journal on Tuesday, the Turkish president has vowed not to allow ISIL fighters to escape northern Syria.
US troop withdrawal
Meanwhile, American troops have prepared to evacuate equipment in advance of a full withdrawal, according to US defence official.
The official, who was not authorised to be quoted by name, said US officials were weighing options for a potential future campaign to counter ISIL, including the possibility of a combination of air power and special operations forces based outside Syria, perhaps in Iraq.
US Secretary of Defense Mark Esper said on Sunday that the withdrawal would be done carefully to protect the troops and ensure that no US equipment was left behind. He declined to say how long that might take.
Bulent Alireza, a Director and Senior Associate at the Turkey Project of the Center for Strategic and International Studies in Washington, told Al Jazeera that the latest Trump moves were "almost embarrassing to watch" and that Pence's planned trip to Ankara was a "mission impossible".
"The Turks will react with scorn," he said. "It's a total misunderstanding of the Turkish psyche."
In Washington, politicians have been increasing the pressure on the administration to take action over Turkey's military operation, now in its seventh day.
Republican Senate leader Mitch McConnell, normally a staunch Trump supporter, said he was "gravely concerned" by events in Syria and Trump's response so far.
Withdrawing US forces from Syria "would re-create the very conditions that we have worked hard to destroy and invite the resurgence of ISIS," he said in a statement.
"Such a withdrawal would also create a broader power vacuum in Syria that will be exploited by Iran and Russia, a catastrophic outcome for the United States' strategic interests."
Following Trump's sanctions announcement, Nancy Pelosi, the House Speaker and a Democrat, said the move on Turkey fell "very short of reversing (the) humanitarian disaster."
Trump reiterated he would pull the remaining US troops out of Syria, apart from a small group in the southern part of the country, and said they would be redeployed elsewhere in the region to monitor the situation.
Republican Lindsey Graham, who is usually a Trump supporter, said late on Monday that he "strongly" supported Trump's sanctions, adding that he intended to "give them reasonable time and space to achieve our mutual goals".
Last week, Graham said he was planning on introducing a bill with Democratic Senator Chris Van Hollen that would impose sanctions on the Turkish military.
Another top Republican, Representative Mike McCaul, said, however, that the sanctions announced on Monday were insufficient.
"We appreciate the administration's planned sanctions, but it does not go far enough to punish Turkey for it egregious offences in Syria," McCaul's office said in a statement.
A statement from Senate Democratic leader Chuck Schumer and Democratic Senators Robert Menendez and Jack Reed said the only person who is able to "immediately stop this tragedy unfolding is the president himself."
"The first step when Congress returns to session this week is for Republicans to join with us in passing a resolution making clear that both parties are demanding the president's decision be reversed," they said.
Esper said on Monday that he would ask NATO allies to take "collective and individual diplomatic and economic measures in response to these egregious Turkish actions".
Battle for Manbij
Meanwhile in Syria, Turkish-backed rebel Syrian forces launched an operation to seize the strategic city of Manbij from Kurdish forces.
Monday's drive came as Syrian government troops started moving towards the country's border with Turkey after Damascus forged an agreement with the SDF to fend off Ankara, in a Russia-brokered deal that once again re-shaped alliances in Syria's multi-layered conflict.
The agreement with the Syrian government marked a major reversal for the Kurdish forces, a long-time ally of the US that was now seen as moving closer to Iran and Russia , Syrian President Bashar al-Assad's main military backers.
A Turkey-backed Syrian rebel fighter gestures to the camera at the border town of Tel Abyad, Syria, October 14, 2019.
The return of Syrian government forces to the region - where the SDF has sought to create an autonomous federation - could further cement al-Assad's hold over the country, and raise the risk of a direct clash confrontation between forces loyal to him and Turkish-led troops.
"For the first time since 2013, the government (of Syria) is back in the northeast," Al Jazeera's Zeina Khodr said from Sanliurfa on the Turkey-Syria border. "They came in. There was no fight. They were invited."
Khodr said that while the situation on the ground was dangerous, negotiations were going on behind the scenes.
Erdogan, meanwhile, played down suggestions that his troops and allies would go to war with Russian-supported Syrian government forces, citing on Monday Moscow's "positive approach".
He added, however, that Turkey's operation against Kurdish forces would intensify, naming Manbij as the next target of the offensive.