The United States has voiced concern about allegations that Syria has transferred long-range Scud missiles to the Lebanese-based militant group Hezbollah.
White House spokesman Robert Gibbs says the U.S. has relayed its concern to the Syrian government.
State Department spokesman P.J. Crowley says any such missile transfer would put Lebanon at "significant risk."
The remarks came a day after Israeli President Shimon Peres accused Syria of supplying Scud missiles to Hezbollah that threaten Israel.
Israel and Hezbollah fought a month-long war in 2006 that killed more than 1,200 Lebanese people and about 160 Israelis. During the war, Hezbollah fired thousands of missiles into Israel, and Israeli forces carried out attacks on Lebanese territory.
The United States has long accused Syria of supporting Hezbollah, which the U.S. considers a terrorist group.
The Obama administration has reached out to Syria in the past year by nominating the first U.S. ambassador to Damascus since 2005 and sending top diplomats to meet with the Syrian president.
The U.S. withdrew its last ambassador to Syria after the assassination of former Lebanese Prime Minister Rafik Hariri in 2005. Many countries have blamed Syria for the assassination, but Damascus has denied any involvement.