Reports suggest explosive is similar to the five letter bombs sent to Ukrainian embassy and other targets in Spain Spanish authorities investigating suspected explosive package found at US Embassy in Madrid © social media

Spanish police reportedly cordoned off the area around the US embassy in Madrid and activated anti-terrorist protocols on Thursday after a letter bomb was allegedly delivered to the building, according to local media.

This comes after five similar letters were sent to various targets across the country, including to the Ukrainian embassy in Madrid, where one worker was injured on Wednesday after opening the package.