Libyan embassy staff have refused a request by protesters to let a representative in to deliver a letter to the ambassador.
The letter calls for the resignation of Libyan leader Muammar Gaddafi and urges the ambassador to declare whether he is still backing the Libyan regime.
"We have a right to go in," a protester complained to an embassy staff member.
The letter was handed to the official amid anger by some of those present.
It is not clear if the ambassador is in the building.