The agency documented 69 civilian casualties in eastern Ukraine in June, including 12 dead and 57 injured -- nearly double the figure for May and the highest figure since August 2015. July saw 73 civilian casualties, including eight dead and 65 injured.
The civilian casualties for June and July nearly doubled the monthly average for the previous nine months, according to OHCHR.
"The escalation of hostilities and the accompanying civilian casualties in eastern Ukraine over the last two months are very worrying," Commissioner Zeid Ra'ad Al Hussein said in a statement.
"The many casualties we have documented in recent weeks suggest that neither Ukrainian forces nor the armed groups are taking the necessary precautions to protect civilians," he said.
More than half the total casualties recorded in the past two months were caused by shelling, while the remaining part were caused by mines, booby traps and improvised explosive devices, according to OHCHR.
"Civilians are once again having to flee to improvised bomb shelters in their basements, sometimes overnight, with increasing frequency," Zeid said. "The price of the ceasefire violations is too high for the women, men and children in eastern Ukraine."
Situation near the front remains volatile
The signing of a ceasefire agreement in February last year in the Belarus capital Minsk hasn't stopped the violence completely. Violations committed by all sides are frequently documented.
Schools and hospitals have been shelled or used by Ukrainian forces and armed groups, and civilian homes have been destroyed or looted, according to OHCHR.
Some of the heaviest shelling over the last 24 hours was in the Avdiivka area, in Donetsk region, where mortar fire was fired during the day and night hours, according to the Ukrainian military.
Electric lines in the area were damaged and the Avdiivka Coke and Chemical Plant are operating in emergency mode, military Spokesman Col. Oleksandr Motuzyanyk said at a briefing Thursday, adding that water supplies to the city could also be interrupted.
UN staff in the city of Donetsk heard sustained exchanges of fire at night and witnessed the damage of a number of homes in the Kuibyshevskyi district over the last weekend, said OHCHR.
"I urge the parties to the conflict to heed the calls of the international community to disengage from the contact line and to adhere to a full and sustainable ceasefire," said Zeid.
"The Government and armed groups in control of certain areas of Donetsk and Luhansk regions must respect applicable international human rights law and international humanitarian law," he added.
Since the beginning of the conflict in April 2014, nearly 9,500 people have been killed in the violence and over 22,100 injured, including Ukrainian armed forces, civilians and members of armed groups, according to UN figures.