It disclosed neither the nature of the charges nor the suspects' identities.
US State Department deputy spokesman Mark Toner told reporters confirmation of the indictments was "an important step towards justice and ending impunity for political assassinations in Lebanon."
Hariri's son and political heir Saad hailed the indictment as a "historic" moment for Lebanon and urged the government of Najib Mikati, dominated by Hezbollah and its allies, to cooperate with the STL.
"After many years of patience, of struggle... today, we witness a historic moment in Lebanese politics, justice and security," Hariri said in a statement.
A judicial official told AFP arrest warrants were issued for four Lebanese suspects, identified by local media as Hezbollah members.
LBC television reported that they include Mustafa Badreddine, brother-in-law of top Hezbollah operative Imad Mughniyeh who was murdered in a 2008 bombing in Damascus.
Badreddine was said to have supervised the Hariri assassination. He had previously been arrested in Kuwait for planning to bomb the US embassy, LBC reported.
Also among the four, LBC said, is Salim Ayyash, a Hezbollah member who holds US citizenship and headed the cell that carried out the bombing.
LBC said Assad Sabra and Hussein Anaissi, also of Hezbollah, were in charge of coordinating with Ahmad Abu Adas, a Palestinian who contacted Al-Jazeera television following the Hariri assassination to say he had carried out bombing.
Hezbollah officials contacted by AFP declined to comment.
But the party's Al-Manar television dismissed the court as "politicised" and said it bore the mark of being at the service of intelligence agencies.
The Iranian- and Syrian-backed group has warned it would "cut off the hand" of anyone who attempts to arrest party members linked to the February 14, 2005 seaside bombing that killed Hariri and 22 others.
Hezbollah forced the collapse of Saad Hariri's Western-backed unity government in January after he refused to stop cooperating with the tribunal.
Mikati, his successor, was appointed with the blessing of Hezbollah, Lebanon's most powerful political and military force.
On Thursday, Mikati issued his government policy statement which failed to clearly spell out whether his cabinet would continue cooperating with the tribunal.
"The government confirms that it will follow the progress of the Special Tribunal for Lebanon, which was set up in principle to see justice served in a manner that is neither politicised nor vengeful, and as long as it does not negatively affect Lebanon's stability and civil peace," read the ambiguously worded statement.
Members of Hariri's "March 14" coalition said the statement was a clear sign Mikati's government would not abide by its international obligations.
"They (the Mikati government) consider that justice would undermine stability and national unity," Fares Soueid, secretary general of the "March 14" opposition, told AFP.
"They picked stability and national unity over justice... while we consider that stability cannot be at the expense of justice."
UN chief Ban Ki-moon called on authorities to cooperate in handing over suspects for trial.
"The secretary general calls on all states to support the independent judicial process, in particular by cooperating with the Special Tribunal in the execution of the indictment and arrest warrants," a spokesperson said in New York.
Lebanon now has 30 days to serve out the arrest warrants. If the suspects are not arrested within that period, the STL can then publicly call on those accused to surrender.
The STL was set up in The Hague in 2009 by the United Nations to try those alleged to have carried out Hariri's killing.
The murder sparked the so-called Cedar Revolution, a wave of mass protests that, combined with international pressure, forced Syria to withdraw its troops from Lebanon after a 29-year deployment.
Syria was widely suspected of having a hand in Hariri's murder but has denied involvement.