The U.N.-backed Special Tribunal for Lebanon is investigating the 2005 assassination of former Lebanese Prime Minister Rafik Hariri.
Hezbollah Secretary-General Hassan Nasrallah said the probe was a ruse meant to upset the political situation in Lebanon.
"It is a political investigation which is masked by a judicial covering and made into a judicial system," he was quoted by Hezbollah's al-Manar news station as saying. "All of these in the past have proved that the special tribunal was used as a political tool."
Brig. Gen. Jamil Sayyed, jailed for four years in connection to the 2005 assassination of former Lebanese Prime Minister Rafik Hariri, said he believes Saad Hariri, the current prime minister and son of Rafik Hariri, paid witnesses to testify against him.
The STL said in September that Sayyed could have "limited" access "to certain materials in the Hariri case."
Nasrallah accused the STL of balking on the issue.
The U.S. Embassy in Beirut last week updated its travel advisory for U.S. citizens as the STL could issue indictments by the end of the year.
"Lebanese political leaders have warned publicly that the tribunal's findings could spark civil unrest or other violence," the advisory read.