ANKARA, Dec. 13 (Xinhua) -- Turkish president announced his army will launch a new military offensive in northern Syria "within a few days," sending signals that Turkey is determined to remove U.S.-backed Kurdish fighters in the region.

"We will start an operation in the next few days to free the east of the Euphrates from the separatist terrorist organization," Recep Tayyip Erdogan said on Wednesday, referring to the territory, east of Euphrates, controlled by Syrian Kurdish People's Protection Units (YPG).

Pentagon voiced "grave concern" over Turkey's imminent military operation in northeastern Syria.

"Unilateral military action into northeast Syria by any party, particularly as U.S. personnel may be present or in the vicinity, is of grave concern," Pentagon Spokesman Sean Robertson said Wednesday. "We would find any such actions unacceptable."

The Turkish president's statement came after the United States is establishing observation posts along the border between Turkey and Syria where the YPG keeps the control, a move that is likely to further strain ties between the two NATO allies.

The posts are designed to help keep the focus on fighting Islamic State (IS) in Syria, U.S. Defense Secretary Jim Mattis said.

"We take Turkish security concerns seriously and we are committed to coordinating our efforts with Turkey to bring stability to northeastern Syria," he stated.

But Ankara is not convinced with U.S. explanation. During a visit by U.S. special envoy for Syria James Jeffrey, the Turkish defense minister asked him to lift these observation posts which Ankara assumes they aim to prevent Turkey targeting YPG positions in the area.

Turkey deems the YPG as an offshoot of the Kurdistan Workers' Party (PKK), which is listed a terrorist organization by Turkey, the United States and the EU.

The YPG, a part of the Syrian Democratic Forces (SDF) alliance, has been a partner in the U.S.-led campaign against the IS in Syria.

"It is clear that the purpose of these U.S. observation posts is not to protect our country from terrorists but to protect terrorists from Turkey," the Turkish president said, adding that U.S. President Donald Trump had promised him to clear the region of the YPG within 30 days. "We will see. We hope that they do it."

"Now, it's time to realize our decision to disperse the circles of terror east of the Euphrates. The fact that we have deep differences in perception with the United States is no secret," the president said.

One day before Erdogan's remarks, the ruling Justice and Development Party (AKP) spokesman Omer Celik expressed skepticism about a U.S. plan to train around 40,000 locals in northeastern Syria.

The move will be seen by Turkey as "lending fresh support to terror elements in Syria," Celik said.

U.S. Chairman of the Joint Chiefs of Staff Joseph Dunford said last week that the United States needs to train and equip around 40,000 local fighters to "provide stability" in Syria.

The support remains a source of tension between Washington and Ankara as the Syrian Kurds gained leverage in northern Syria with arms support of the United States since civil war erupted in the country in 2011.

The U.S. decision to deploy observation posts in northern Syria along with Turkish border came after the Turkish Armed Forces fired artillery shells at YPG positions east of the Euphrates in the Kobane region in November.

Anadolu Agency reported that Turkish howitzers hit YPG targets in Zor Magar region along the Turkish-Syrian border line.

Since 2016, The Turkish military has already launched two military operations in Syria and it has an undisclosed number of troops in several Syrian regions, mainly to block advance of Syrian Kurds in the region.

Turkey sent troops to Syria in August 2016 to clear a border area of fighters belonging to the IS and prevent bridging Kurdish regions in the east and west.

The Turkish army launched another operation earlier this year in the northern Syrian enclave of Afrin to remove Kurdish fighters.

Turkey's target is never the U.S. soldiers, but rather the members of the YPG group, Erdogan said, adding that "this step will allow for the path to a political solution to be opened and for healthier cooperation."

Experts warn against such move by Turkish army in the region would bring high risks since the U.S. soldiers in the area could cause a confrontation between the two NATO allies.

"It would be a military offensive with high risks. There are American soldiers in the area, along with French ones," Ugur Sevkat, a military-focused commentator of NTV broadcaster said.

He also recalled that the United States has been providing arms support to the YPG for the past few years, and the content of these weapons are not transparent, but reportedly some 20,000 trucks carried the logistics for the Kurdish group.

Sevkat noted there is a 500-km-long border of Turkey with the specified area of northern Syria, which requires a remarkable military buildup for the border troops of Turkey.

"In the past few days there are a small scale of military reinforcement for these border troops, but not at a scale that is needed for a comprehensive military offensive. Therefore, we can assume Turkey will not launch a major military campaign here," he said.

If the Turkish army moves into "small pockets" into Syria, it will show it's determination and convince the United States for a solution, according to the expert.