KABUL, Afghanistan — The number of civilians killed or injured in Afghanistan rose by nearly a quarter in the first six months of 2013, according to a U.N. report, reversing a decline last year that many hoped would signal an easing in the war’s toll on ordinary Afghans.

The Taliban continued to cause the vast majority of those casualties, with the factors driving the 23 percent increase including the indiscriminate use of roadside bombs and suicide attacks in major population centers, according to the report, released Wednesday.

From January to June, the number of civilians killed in war-related violence rose to 1,319 from 1,158 a year earlier. In the same period, 2,533 civilians were injured, compared with 1,976 in 2012. For deaths, 2011 remains the worst year for Afghan civilians, with 1,575 killed in the first half of that year.

As Afghan forces have taken the lead in fighting this year, the insurgency has hit them hard, seeking to undermine confidence in Afghan government institutions as the coalition forces prepare to withdraw. That effort has included a focus on complex attacks in major cities like Kabul, where Afghans often find themselves in harm’s way, as well as other measures that have been felt mostly by civilians.

The shifting political and security situation has also led to increased ground fighting between the Afghan forces and insurgents, as the international troops shut down bases and reduce their footprint across the country. Fighting between the two groups over the abandoned swaths of the country was the second-biggest cause of civilian deaths and injuries.

Anti-government forces using improvised explosive devices accounted for more than a third of the civilian casualties in the first half of 2013. Women and children, in particular, suffered. Ground battles were the leading contributor to a 60 percent jump in casualties among women, while improvised explosive devices largely caused a 30 percent increase in injuries and deaths of children.

A Taliban spokesman, Zabiullah Mujahid, would not comment on the report, saying the insurgents have formed a commission to review it. But there is little doubt the numbers will put greater pressure on the Taliban, from communities and its own ranks, to reduce the carnage among civilians.

Since the Afghans will continue to take a greater role in security operations, the United Nations expressed concern about “the absence of functioning oversight and accountability mechanisms.” When confronted with evidence of civilian casualties, the report said, the Afghan National Security Forces responded “that they did not know about the incident, or that the incident did not happen, or that the incident occurred but ANSF were not responsible.”