Hezbollah leaders during the summer said they believed some of their members could be indicted by the U.N.-backed Special Tribunal for Lebanon.
The STL is investigating the 2005 assassination of former Lebanese Prime Minister Rafik Hariri, who was killed in a massive bombing in downtown Beirut along with 22 others.
Syria and Hezbollah are widely believed to have played a role in the plot. Saad Hariri, the current prime minister and son of the slain leader, recently absolved Damascus and Hezbollah said it has evidence to suggest Israel played a role in the assassination.
The Wall Street Journal reported this week that at least two members of Hezbollah could be indicted by the STL before the end of the year.
Hezbollah Secretary-General Hassan Nasrallah warned in a late Thursday speech not to arrest or detain any of his supporters.
"Whoever thinks that we will allow the arrest or detention of any of our mujahedin is mistaken," Hezbollah's al-Manar satellite channel quoted him as saying. "The hand that attempts to reach them will be cut off."
Hezbollah objected to STL investigators who were questioning employees at a women's clinic near Beirut, complaining the tribunal was spying.
Nasrallah added that the reputation of the Shiite movement was at stake in the STL probe.
"Whoever thinks that the resistance will not defend itself and its honor against any accusation or attack by whatever means it finds appropriate, in agreement with its allies in Lebanon, is mistaken," he said.