In the report to the United Nations Security Council, Ban Ki-moon said the increased tension was "fueled among other things by speculation and public pronouncements concerning the proceeding of the Special Tribunal for Lebanon," a UN spokesman said.

He warned that increasingly entrenched positions for and against the tribunal were polarizing the country, the spokesman Farhan Haq said.

The UN chief also emphasized that the proliferation of weapons outside the state's control and the presence of heavily armed militias were a threat to the country's peace and prosperity.

"The secretary general remains convinced that the disarmament of armed groups in Lebanon, in particular the Hezbollah, can best be achieved through a political process," said Haq.

"He calls on Lebanese leaders to reconvene the national dialogue under the auspices of President Michel Sleimane," he said.

The tribunal's prosecutor, Daniel Bellemare, on Friday filed an amended indictment based on further evidence in the probe into the Hariri assassination, his office said.

The indictment, which is being kept confidential, has to be examined by Belgian judge Daniel Fransen, who has the responsibility of confirming it before arrest warrants or summonses are issued.

Hezbollah is the only group that has not laid down its arms since the end of the Lebanese civil war in 1990, insisting it needs its arsenal to fight Israel.

The powerful Shiite movement has let it be known repeatedly that disarmament is not on the table for discussion.

Palestinian factions based in refugee camps in Lebanon, which the Lebanese army does not enter, are also armed.