Concerns were raised this week about a shipment, allegedly carrying weapons to Syria, that left Russia. Moscow maintains a military trade relationship with Damascus despite ongoing bloodshed in the country.
Susan Rice, the U.S. ambassador to the United Nations, said, without mentioning specific countries, that Washington was concerned by reports of shipments of weapons to the Syrian government of President Bashar Assad. Washington, she added, called on any suppliers to halt deliveries to the regime voluntarily.
A monitoring team from the Arab League this week said it would consult with the United Nations about the ongoing bloodshed in Syria. Several monitors pulled out of the mission because of the violence.
Rice said it was "essential" that the international community coordinate on the Syrian crisis.
"The situation there continues to deteriorate dramatically," she added. "Despite the presence of Arab League monitors, the Assad regime is ignoring its commitments to the Arab League plan, including by failing to end all acts of violence and to protect Syrian civilians."
Syria maintains it is dealing with an armed insurgency supported by foreign elements. The United Nations estimates at least 5,000 people were killed by security forces since March.
"We hold the Syrian regime fully responsible for the worsening cycle of violence," said Rice.