"I think we are making headway," Robert Gates, the US defence secretary, had said on Wednesday.
"I think we are regaining the initiative."
However, the study found some encouraging signs, including the government's plan to reach out to anti-government fighters and offer economic incentives to leave the battlefield.
The number of civilians killed or wounded by international forces had also dropped by 44.4 per cent in the past 12 weeks, compared with the same period in 2009.
Haroun Mir, the co-founder and deputy director of the Kabul-based Centre for Research and Policy Studies, agreed with the UN assessment of the security situation.
"I think that security has worsened significantly since last year," he told Al Jazeera.
"Now in some of the northern provinces, travelling to them is very risky."
Brigadier General Josef Blotz, a Nato spokesman, told reporters that despite negative assessments, the international force was making steady strides.
"Tough fighting is expected to continue, but the situation is trending in our favour as more forces flow into the area," Blotz said.
"It has to be tougher perhaps before it goes easier," he said.
The increased violence comes at a time when more US troops are moving into Afghanistan as part of a surge orchestrated by Barack Obama, the US president.
There are currently an estimated 142,000 troops in Afghanistan and that number is expected to peak at 150,000 in August, before a planned withdrawal in 2011.