A small bomb exploded Saturday near the Tomb of the Unknown Soldier in front of Parliament in central Athens, police said. No one was injured. The blast occurred at 7:59 p.m. local time (1759 GMT) and was heard across Athens' Syntagma Square. An anonymous caller had telephoned a warning to a national newspaper 17 minutes earlier. Police cordoned off the area before the blast, shutting down a major avenue in the center of the capital. About an hour later, the nearby 5-star Grande Bretagne hotel received a bomb threat. Police said the bomb was placed in a trash can. Following the blast, hundreds of police were deployed around the Parliament and Syntagma Square, shouting at passers-by to stay clear. But the guards in front of the tomb did not budge although the blast occurred just a few meters away. The Parliament is not in session, but lawmakers from the ruling Socialist party were meeting with the Minister of the Interior at the time. "We heard the blast, but we continued our meeting. We are not worried," lawmaker Christos Protopapas told the Associated Press. Several extremist left-wing groups operate in Greece, and they often plant bombs targeting businesses, government offices and banks. The bombs are usually planted late at night or preceded by warning calls and rarely cause casualties. Police experts said placing the bomb in such a central location could be seen as a challenge to the new government, which stepped up security measures in October after winning power.