"The prosecutor of the tribunal has submitted an indictment and supporting materials to the pre-trial judge," the UN-backed tribunal (STL) said in a statement from Leidschendam, near The Hague, where it is based for security reasons.
"The contents of the indictment remain confidential at this stage."
In expectation of being named, Hezbollah warned on Sunday it would "defend" itself and branded the tribunal a tool of the United States and Israel.
"We will not allow our reputation and our dignity to be tarnished nor will we allow anyone to conspire against us or to unjustly drench us in Hariri's blood," Hezbollah chief Hassan Nasrallah said in a televised speech.
The Shiite militant group which enjoys the backing of Iran and Syria, withdrew from the Lebanese cabinet with its allies on Wednesday, citing the UN-backed probe, prompting the collapse of the unity government led by Western-backed Prime Minister Saad Hariri, son of the murdered former premier.
Lebanon's president on Monday postponed talks on naming a new prime minister, as regional leaders threw their weight behind a Syrian-Saudi bid to defuse the crisis.
Turkish Prime Minister Recep Tayyip Erdogan, Qatari Emir Sheikh Hamad bin Khalifa al-Thani and Syrian President Bashar al-Assad met in Damascus on Monday for talks on the deadlock.
The three leaders "expressed their commitment to a solution to the Lebanese crisis based on Syrian-Saudi good offices, so as to... avoid a deterioration of the situation", the Syrian SANA news agency reported after the meeting.
Iran's acting Foreign Minister Ali Akbar Salehi was also to hold talks on the crisis with Erdogan in Turkey later on Monday.
Turkish Foreign Minister Ahmet Davutoglu was to travel to Lebanon on Tuesday to help mediate in the crisis, a diplomat said in Ankara.
UN chief Ban Ki-moon, on a visit to Abu Dhabi, called for calm in Lebanon and made an appeal for the work of the tribunal not to be politicised.
Meanwhile Lebanon's acting foreign minister said he had summoned the US ambassador on Monday for interfering in the country's crisis-hit domestic politics after she met with a Christian lawmaker.
The US State Department denied the charge.
The special tribunal was created, at Lebanon's request, by a 2007 UN Security Council resolution to find and try Hariri's killers.
According to its rules of procedure, the indictment will be reviewed by pre-trial judge Daniel Fransen, who must confirm the charges before any arrest warrant or summons to appear can be issued.
The judge may also reject the indictment in whole or in part, or ask the prosecutor for additional information.
Fransen should need six to 10 weeks to confirm the charges, after which a trial could start within four to six months.
The STL's rules allow for a trial to be held in absentia, if arrests are impossible.
Prosecutor Bellemare's office, meanwhile, said he would elaborate on the "significance" of the indictment in a videotaped statement to be released on Tuesday.
"The prosecutor and his team will continue to vigorously pursue his mandate with respect to both continued investigative activity and the prosecution of this case," it said.
Hezbollah, "Party of God" in Arabic, has warned it would "cut off the hand" of anyone who tries to arrest any of its members over the Hariri killing, raising fears of renewed Sunni-Shiite sectarian violence, 20 years after the end of a 15-year civil war.
The tribunal opened its doors in The Hague in 2009, four years after Hariri's murder triggered a political crisis that caused the withdrawal of Syrian troops after a 29-year presence in Lebanon.
Damascus has consistently denied involvement in the killing.
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