"It seems to me that these allegations are made by people who may fear the outcome of the tribunal's decision or of the tribunal's effort to uncover the truth," he said.
The STL was created by a 2007 UN Security Council resolution to try the killers of Hariri, assassinated in a massive car bombing on the Beirut seafront on February 14, 2005 that also killed 22 other people.
Foreign media, most recently the Canadian public broadcaster CBC, have widely reported that Bellemare's ongoing probe is likely to result in charges against the Hezbollah militant group.
The Shiite movement, which dismisses the tribunal as part of a US-Israeli plot, has said it would not accept the indictment of its members and warned of repercussions -- raising regional fears of renewed Sunni-Shiite sectarian violence and the collapse of Lebanon's hard-won national unity government.
The pending indictment has split Lebanon's unity government, pitting Hezbollah against a camp led by Western-backed Prime Minister Saad Hariri, son of the assassinated Sunni leader.
Hezbollah carries the backing of Iran and of Syria, while Saudi Arabia backs the Lebanese premier.
"The evidence is my only guide," Bellemare insisted on Wednesday.
"The fact that this institution was created by a political body or the fact that we operate in a highly politicised environment does not mean that we are politicised.
"The two main protections against politicisation are independence and professionalism."
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