Dozens of US State Department officials have signed an internal memo protesting against US policy in Syria and calling for targeted military strikes against President Bashar al-Assad's government.
They argue the current approach is working against the Syrian opposition and helping Mr Assad to stay in power.
It was signed by 51 mid-to-high level officials who advise on Syria issues.
It is not unusual for internal "dissent cables" to be filed through State Department channels.
However, it is rare to have this number of diplomats voice opposition to a White House position.
A State Department spokesman acknowledged receipt of the memo but declined to comment on its contents.
However, an official familiar with the letter told the BBC that it was sent "because the status quo is not sustainable".
The document urges a credible threat of military action against the Assad government. Otherwise, it says, Damascus will feel no pressure to negotiate with the rebels.
This reflects concerns that the collapse of a joint US-Russian peace process is benefitting the regime.
There have been violations of the ceasefire by both the opposition and the government.
But President Assad has openly defied the truce, and his forces, backed militarily by Iran and Russia, seem intent on regaining strategic territory such as the crucial city of Aleppo.
