The United Nations on Wednesday extended the mandate of the special tribunal investigating the 2005 assassination of former Lebanese prime minister Rafiq Hariri. The tribunal faces strong opposition from the Hezbollah party in Lebanon, but in announcing the three-year extension of the inquiry, UN leader Ban Ki-moon said he was determined to \"send a message that impunity will not be tolerated.\" The work of the Special Tribunal for Lebanon has now been extended for three years from March 1, UN spokesman Martin Nesirky said in a statement. The tribunal was set up by the UN Security Council in 2007 and has announced that it will put four Hezbollah members on trial even though they have not yet been detained. The four -- Salim Ayyash, Mustafa Badreddine, Hussein Anaissi and Assad Sabra -- have been charged for the February 14, 2005 car bombing in Beirut that killed Hariri and 22 others, including a suicide bomber. Warrants have been issued for the four, but authorities in Lebanon, where the government is dominated by the Iranian- and Syrian-backed Hezbollah, have failed to arrest them. The United Nations is preparing to announce a replacement for the tribunal\'s chief prosecutor, Daniel Bellamare, who will leave at the end of the month. But Ban visited the court in Lebanon last month in one sign of support. And the announcement of the mandate extension included a new signal of support from the UN leader. \"The secretary general reaffirms the commitment of the United Nations to the efforts of the Special Tribunal for Lebanon to uncover the truth regarding the terrorist attack\" that killed Hariri \"so as to bring those responsible to justice and send a message that impunity will not be tolerated,\" said the UN statement.