Syria’s Foreign Ministry on Monday slammed the plan as a "blatant assault" on its sovereignty.
State television cited an official source in the ministry as saying that the Syrian army is resolved to end any form of US presence in the country.
The US, purportedly fighting the Daesh terrorist group, is planning to build the so-called "Border Security Force" on the Syrian territory held by the so-called Syrian Democratic Forces (SDF) which is dominated by Kurdish militants.
Russian Foreign Minister Sergei Lavrov said Washington’s decision to form a zone held by US-backed militants could lead to the division of the Arab country.
"The announcement that this zone will be controlled by the US-backed groups - by the force up to 30,000 people - this is a very serious issue, which causes concerns that a course was set for the partition of Syria," Lavrov said at an annual news conference.
The US, he said, is helping those who are seeking to topple the government of Syria rather than trying to resolve the Syrian crisis.
"We don't see the efforts to help resolve the conflict as soon as possible, but rather to help those who would like to make practical steps to change the government in Syrian Arab Republic," Lavrov added.
Syria has been gripped by foreign-backed militancy since March 2011. The Syrian government says the Israeli regime and its Western and regional allies are aiding Takfiri terrorist groups that are wreaking havoc in the country.
Moscow vows to react to US border force
Lavrov's remarks came a day after Chairman of the Defense Committee of Russia’s State Duma Vladimir Shamanov vowed to take measures in reaction to Washington’s decision to deploy the so-called "Border Security Force".
Shamanov said the US plan "stands in direct confrontation" with Russia's interests. "We and our colleagues will certainly undertake certain measures on stabilization of the situation in Syria," he said.
Turkey says US 'playing with fire'
The US move has also angered Ankara with Deputy Prime Minister Bekir Bozdag saying on Monday that Washington is "playing with fire".
Turkey is already angry over strong US support for Kurdish forces in Syria. Ankara views SDF and its affiliates as the Syrian branch of the Kurdistan Workers' Party (PKK), which has been fighting Turkey since 1984.
The US launched its military campaign in Syria in 2014 under the pretext of fighting Daesh terrorists. Syria and Russia as well as other regional countries have cast doubt on the United States' true intentions, saying American troops have mostly tried to hamper government operations against Takfiri terrorists and harmed the country's infrastructure.
Syria calls the "coalition" led by the US “an illegal occupation force” which has entered the country without its permission or a UN mandate. It also views Washington's SDF allies as “traitors”.
Foreign Minister Lavrov last month said the presence of American troops in Syria was unlawful, urging them to completely leave the Syrian soil.