President Joseph Kabila agreed to free political prisoners and respect the rights of the opposition under a political deal reached in 2016, but Zerrougui said the government had fallen short of those commitments.
"A failure to generate confidence in the full and faithful implementation of the December 31 agreement will only serve to heighten political tensions, and to fuel the risks of inciting violence for political ends," said Zerrougui.
After much delay, authorities in the vast mineral-rich African country set a date of December 23 for elections that are expected to pave the way to a historic transfer of power.
But Kabila, who took over from his father Laurent after he was assassinated in 2001, has not yet clearly stated whether he will step aside.
Anti-government protests have turned deadly over the past months, despite UN appeals to Kabila to rein in his security forces.
Zerrougui said the "disproportionate use of force by security services" during protests in December and January were a "major concern" after 16 people were killed, more than 100 were wounded and dozens more arrested.
Security has deteriorated in eastern DR Congo, where rebel groups have attacked Congolese forces and UN peacekeepers, while militias in the Kasai region are increasing their activities, said Zerrougui.
The Security Council was meeting as it prepares to renew the mandate of its 17,500-strong peacekeeping mission in the DR Congo, known as MONUSCO.
Zerrougui urged the top UN body to ensure that MONUSCO supports the political and electoral process in the country and help stabilize the security situation.
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