Syria’s most senior diplomat in Washington has been summoned to the state department to explain the country’s “provocative behaviour” in apparently transferring scud missiles to Hizbollah.
Zouheir Jabbour, the deputy chief of mission for Syria in Washington, was told that the US condemned his country’s actions.
US state department spokesman Gordon Duguid said: "This was the fourth occasion on which these concerns have been raised to the Syrian embassy in recent months, intended to further amplify our messages communicated to the Syrian government.
"The United States condemns in the strongest terms the transfer of any arms, and especially ballistic missile systems such as the Scud, from Syria to Hizbollah.
"The risk of miscalculation that could result from this type of escalation should make Syria reverse the ill-conceived policy it has pursued."
The UN Security Council resolution which ended the 2006 conflict between Israel and Lebanon included an arms embargo on Lebanon, except for government and UN movements.
Hizbollah is widely believed to be strengthening its weapons arsenal with help from Syria and Iran.
The US does not have an ambassador to Syria, and has not had one since 2005 when it withdrew its envoy over the killing of former Lebanese Prime Minister Rafik Hariri, which was blamed on Syria.
However, the White House has been making moves towards restoring diplomatic communication and a nomination for the post of ambassador to Syria is currently going through the Senate.