UNITED NATIONS, Jan. 16 -- UN Secretary-General Ban Ki- moon Thursday welcomed the start of the trial of four suspects accused of killing former Lebanese Prime Minister Rafik Hariri in a blast.

"The secretary-general welcomes the opening today of the trial of the Special Tribunal for Lebanon (STL), nearly nine years after the heinous terrorist attack which killed former Prime Minister Rafiq Hariri and 21 others," said a statement issued here by Ban's spokesperson.

"The secretary-general stresses the vital importance of combating impunity for the long-term stability and security of Lebanon," the statement said.

"He notes with gratitude the continuing support of the Government of Lebanon, and of other Member States, for the work of the Tribunal," it added.

The trial began in The Hague on Thursday with opening statements by chief prosecutor Norman Farrell.

A case has been brought against four suspects for the assassination of Hariri, who was killed in February 2005 when a bomb exploded in the Lebanese capital of Beirut. The explosion killed 22 individuals and injured 226 others.

The proceedings against the four accused are being held in absentia because they are still at large. The indictment and accompanying arrest warrants were transmitted to the Lebanese authorities on June 30, 2011.

The four accused, Mustafa Badreddine, Salim Ayyash, Hussein Oneissi and Assad Sabra, are said linked to Lebanon's militant and political Hezbollah movement, according to media reports.