Hezbollah called for a boycott of the STL because it says the investigation is part of an Israeli ploy meant to discredit the Shiite opposition movement. Lawmakers loyal to Hezbollah said last week that tribunal investigators were encroaching on the privacy of several members tied to the Lebanese government.
STL President Antonio Cassese in his annual report on the tribunal's work said it has carried out its activity with the utmost respect for impartiality.
"To this effect, we must act in such a manner as to indisputably show that we are immune from political or ideological bias and at any moment respect," he wrote in his report.
Cassese said it was important to remember that Lebanon was one of the parties that called for the development of the tribunal to investigate the 2005 assassination of former Lebanese Prime Minister Rafik Hariri.
Critics said the tribunal's findings could spark conflict in Lebanon, which is still recovering from decades of civil war. Cassese in his report said that opposition was expected when considering the consequences that the tribunal could have on international justice but said justice was needed for Lebanese reconciliation.
"This is not because we are inherently blind to political sensitivities but because the mission entrusted upon us by the founding instruments of the Special Tribunal requires us to consider the long haul, not contingent political games and considerations," he wrote.