The US repeated calls on Wednesday for sanctions against foreign companies that have ties to Syrian President Bashar Al Assad's regime.
Syria has suffered immense damage and physical destruction after nearly eight years of civil war has killed hundreds of thousands of people.
“We reiterate our warning that anyone doing business with [the] Assad regime or its associates is exposing themselves to the possibility of US sanctions,” the US Embassy in Syria said on Twitter.
The warning comes as Damascus held the 61st round of its International Trade Fair, which was suspended after the war started in 2011, but resumed in 2017.
The fair aims to encourage foreign investment to assist in the reconstruction of the war-torn country.
About 500 companies are expected to take part, Syrian state news agency, Sana, reported.
But the government needs billions of dollars for the reconstruction. The United Nations estimates the cost at $250 billion (Dh918bn), whereas the World Bank predicts a $780 billion cost if the war continues until 2021.
The US and European states say they cannot provide aid for reconstruction in Syria without a political transition and end to the war.
"The fair sends a direct message of Syrian victory to the world especially against attempts of isolating the country," the agency said.
Washington has repeatedly said that it is “unacceptable and inappropriate” for businesses and chambers of commerce to participate in the trade fair with the Syrian regime.
Especially "at a time when the Assad regime and its allies Russia and the Islamic Revolutionary Guard Corps are attacking innocent Syrians,” the embassy said.
The development comes as the Syrian army is continuing its battle against rebel groups in the north.
"The Assad regime continues to use its financial resources to carry out vicious attacks against the Syrian people," the embassy said. Anyone doing business with Mr Al Assad "will be enabling the regime to continue its campaign of murder and oppression", it said.
After eight years of conflict, Syrian government forces backed by Russia are several months into an operation to quash armed opposition groups and extremists in the north-west province of Idlib.
Victory for Mr Al Assad would all but mark the end of the military phase of the war in Syria, which erupted after his forces brutally suppressed a series of peaceful, anti-government protests in 2011.
At the same time, the violence has displaced more than 400,000 people including many already uprooted from other areas since last April, the United Nations said.
The Syrian war has killed more than 370,000 and displaced millions of people.