Dozens of police and anti-riot forces stationed in front of the embassy in the centre of Tehran preventing the protestors from getting into the embassy.
Security forces also set up fences around the walls in order to protect the embassy’s compound, witnesses said.
The seven sailors and eight Royal Marines were seized March 23 from a British patrol boat in the Shatt al-Arab waterway, triggering the diplomatic row between Tehran and London.
London insists that the British Navy vessel was legally in Iraqi waters.
