"I was personally informed by Prime Minister (Saad) Hariri that the tribunal will accuse some undisciplined members" of Hezbollah, Hassan Nasrallah said in a press conference via video link.
"I will declare that Hezbollah had nothing to do with it (assassination)," added Nasrallah.
Reports published over the past few days said tribunal prosecutor Daniel Bellemare plans to indict Hezbollah members.
On Thursday the Al-Arabiya network reported that Bellemare met with representatives of the UN Security Council at the British Embassy in New York and told them he would file indictments against Lebanese figures by the end of the year.
"We must understand that Lebanon is entering a very sensitive and complicated phase," Nasrallah told the press conference. "This is not due to internal circumstances or a war with Israel, but because of a report that will soon be published by the international tribunal."
According to Nasrallah, Lt.-Gen. Gabi Ashkenazi, whom he calls the "enemy's" chief of staff, has already presented the various "scenarios for the situation in Lebanon following the conviction."
"There is an elaborate plan to hurt the resistance (i.e. Hezbollah), after all previous plans have failed," he added.
In a speech earlier this month, Nasrallah accused Israel of interfering in the probe and slammed the tribunal's impending indictment as "fabricated."
Media reports last year said that evidence implicated Hezbollah in the assassination of former premier Hariri in a massive seaside bombing on February 14, 2005.
Nasrallah in March confirmed UN investigators had interrogated members of his Syrian- and Iranian-backed party but said at the time that Hezbollah was not in the tribunal's line of fire.