US President Barack Obama on Tuesday arrived in Athens for a two-day visit amid draconian security measures as his trip marks the first to the country by a US leader since 1999.A large part of the Greek capital has been locked down, and snipers are deployed on rooftops and public gatherings have been banned, Xinhua news agency reported.Despite the ban, the Communist Party-affiliated union PAME and other trade unions have called for protests on Tuesday.Some 4,500 Greek police officers are participating in the security operation, together with 300 US security personnel.Greek President Prokopis Pavlopoulos will welcome the outgoing President at the Presidential Mansion and then Obama will have talks with Prime Minister Alexis Tsipras.The first day of the visit will end with an official dinner hosted by Pavlopoulos.On Wednesday, the US President is expected to visit the Acropolis and deliver a speech at Stavros Niarchos Foundation Cultural Centre before leaving Greece to continue his current Europe tour.