• UN report says 3,021 civilians killed in 2011 • 8% increase on 2010 and fifth consecutive rise • Number of suicide bombings static but toll rises 80%

The civilian death toll for the war in Afghanistan reached a record high last year with 3,021 deaths, according to the United Nations.

The number killed rose by 8% last year – the fifth consecutive rise – with a further 4,507 civilians wounded, the UN report said. Many were killed by roadside bombs or in suicide attacks, with Taliban-affiliated militants responsible for three-quarters of the deaths.

The number of deaths caused by suicide bombings jumped to 450, an 80% increase over the previous year, even though the number of suicide attacks remained about the same.

"A decade after the war began, the human cost of it is still rising," said Georgette Gagnon, director for human rights for the UN mission in Afghanistan.

The single deadliest suicide attack since 2008 occurred on 6 December, when a bomber detonated his explosives-filled vest at the entrance of a mosque in Kabul, killing 56 worshippers during the Shia Muslim rituals of Ashoura.

Roadside bombs remain the biggest killer of civilians. The homemade explosives – which can be triggered by a footstep or a vehicle and are often rigged with enough explosives to destroy a tank – killed 967 people in 2011, nearly a third of the total.

The figures come as Nato begins to map out plans for international troops to withdraw and hand over responsibility for security to Afghan security forces.

The presence of western forces has managed to reduce civilian casualties in the troubled southern provinces of Helmand and Kandahar. But the UN found that insurgents had focused instead on areas along the country's border with Pakistan. They were also relying more on roadside bombs and suicide attacks in places like bazaars, school grounds, footpaths and bus stations.

"The tactics have changed," said Jan Kubis, the UN secretary general's special representative to Afghanistan. "The anti-government forces being squeezed in certain areas ... move to some other areas and again use these inhuman, undiscriminating weapons like human-activated explosive devices and suicide attacks."

Kubis said the Taliban banned the use of land mines as "un-Islamic and anti-human" in 1998 when they ruled Afghanistan with their harsh interpretation of Islamic law. But the UN report said there was little difference between mines and the buried homemade bombs used by the Taliban. The majority of improvised devices have about 20kg (44lb) of explosives and are triggered when a person steps on, or a vehicle drives over rigged pressure plates.

"These are basically land mines," Kubis said of the roadside bombs. "So why is this 'inhuman and un-Islamic' weapon being increasingly used?"

The number of roadside bombs planted last year overwhelmed security forces' improved ability to detect and defuse them. An average of 23 roadside bombs a day were either detonated or discovered and defused last year, twice the daily average in 2010, the report said. Actual explosions increased by 6%.

The UN attributed 77% of the deaths to insurgent attacks and 14% to actions by international and Afghan troops. The cause of the remaining 9% were classified as unknown.