The United States accused the Lebanese militant group Hezbollah on Friday of a deep involvement in the Syria government’s violent campaign to crush the uprising there, asserting that Hezbollah has trained and advised government forces inside Syria and helped to expel opposition fighters from areas of the country.

The American accusations, which were contained in coordinated announcements by the Treasury and State Departments announcing new sanctions on Syria, also accused Hezbollah of helping operatives of Iran’s Revolutionary Guards Quds Force in training Syrian forces inside Syria. A Treasury statement said Hezbollah’s secretary general, Hassan Nasrallah, had overseen these activities, which it called part of the Syria government’s “increasingly ruthless efforts to fight against the opposition.”

The accusations went beyond previous American claims about Hezbollah support for Syria’s government. They seemed designed to counter Obama Administration critics who say the White House is not doing enough to back the Syrian opposition. They were also part of an effort to further draw attention to the alliance of Hezbollah and Iran, which American and Israeli intelligence officials have sought to portray as a subversive collaboration that has not only destabilized the Middle East but has been implicated in terrorist violence elsewhere, including a deadly bus bombing of Israeli tourists in Bulgaria last month.

The accusations also came a few days after Iran’s top national security official, Saeed Jalili, visited Syria and assured its embattled president, Bashar al-Assad, that Iran, Syria and Hezbollah were an unbreakable axis of resistance to Israel and its Western allies, reinforcing Syria’s evolving role as the arena of a proxy war pitting Iran and its friends against the West.