The mob forced its way into the meeting on the grounds of a Colombo Catholic church, where families of disappeared persons from the civil conflict were sharing their stories with civil society groups and members of the diplomatic community, Embassy said in a statement.
The Embassy charged that the initial reaction of the local police to this disruption appeared to be in support of the mob efforts to shut down the meeting.
"The strong impression was that the protesters were seeking to intimidate and silence those in attendance," it said.
The United States strongly urged the Government of Sri Lanka to enforce the rule of law and permit all citizens to exercise their most basic human rights, including freedom of speech and freedom of assembly.
The Embassy also called on the Government of Sri Lanka take all possible steps to ensure the safety of families who had traveled from the North to attend this meeting, both in Colombo and upon their return home.