A day after President Donald Trump announced he would withdraw U.S. troops from northeastern Syria, Turkey on Tuesday said it is moving ahead with military operations in the country targeting Kurdish forces.

"All preparations for the operation have been completed," Turkey's defense ministry said.

The Syrian Democratic Forces (SDF) reported on Twitter that Turkey had begun shelling an SDF post in a border city, but said none of its forces were injured and that it had not responded to "this unprovoked attack."

The Turkish military is shelling one of our points on #SereKaniye Border with Turkey. There were no injuries to our forces.

We didn't respond to this unprovoked attack. We are prepared to defend the people and the people of NE #Syria.@mutludc @mustefabali @vvanwilgenburg — Coordination & Military Ops Center - SDF (@cmoc_sdf) October 8, 2019

Late on Monday, the U.K.-based Syrian Observatory for Human Rights countered reports that bombing by Turkish forces had already begun that day.

Reports that Turkish troops and tanks were assuming positions along the Turkey-Syria border was causing tension in the border city of Akcakale Tuesday, according to Al Jazeera.

"There's a lot of tension here," said Al Jazeera reporter Charles Stratford. "There are huge concerns about the security ramifications this operation could have. It's very difficult to predict when any military operation might start."

The SDF, which includes many Kurdish fighters and which spent years helping the U.S. to combat ISIS in the region, said troops were standing ready to fight a possible Turkish attack—without the help of the United States.

"We as Syrian Democratic Forces take the matter into account and are fully prepared to fiercely respond to any imminent attack on Syrian soil," SDF spokesman Gabriel Kino told Al Jazeera.

Trump said Monday that "having defeated the ISIS territorial 'Caliphate,'" the U.S. Armed Forces will no longer be in northeastern Syria—defying the advice of his own military officials.

Syria's deputy foreign minister Faisal Mekdad called on Kurds in Syria to rejoin government forces after Trump's announcement.

"The homeland welcomes all its sons, and Damascus will solve all Syrian problems in a positive way, away from violence," Mekdad told the newspaper Al-Watan.

Rep. Alexandria Ocasio-Cortez (D-N.Y.) tweeted Tuesday that Trump's decision to withdraw troops from northeastern Syria "could have catastrophic consequences" for the civil war there and "risks laying the ground for immense violence and suffering."