Two NATO soldiers were killed in an attack in Afghanistan Sunday as alliance leaders gathered in Chicago for a summit dominated by plans to pull troops out of the Afghan war.

Two children also died and several civilians were wounded as a suicide bomber targeted a NATO convoy in Tirin Kot, capital of southern Uruzgan province, Afghan police said.

At least 162 troops with NATO's International Security Assistance Force (ISAF) have died in Afghanistan this year, according to an AFP count based on the website icasualties.org.

More than 3,000 have been killed since the US led an invasion to topple the Taliban regime in late 2001.

"Two International Security Assistance Force service members died following an insurgent attack in southern Afghanistan today," ISAF said in a statement, without giving further details.

Two children were also killed, the Uruzgan provincial police chief told AFP.

"In a suicide attack against an ISAF convoy in Tirin Kot this morning two children were killed and several other civilians were wounded," said General Matiullah Khan.

The number of civilians killed in the Afghan war has risen steadily each year for the past five years, reaching a record of 3,021 in 2011, the great majority caused by militants, according to UN statistics.

The Taliban this month announced the start of their annual spring offensive, a campaign of bombings and attacks that picks up every year as the weather warms.

On Friday, a rocket attack by Taliban insurgents on a NATO base in the eastern Afghan province of Kunar killed two international soldiers and wounded six.

On Saturday, a suicide bomber struck at a lunch gathering of Afghan police and local civilians in southeast Afghanistan, killing at least 13 people, three of them policemen.

Despite the stubborn Taliban insurgency, war-weary international forces are seeking to hand control of security to Afghan forces while withdrawing their combat troops by the end of 2014.

In Chicago, NATO is likely to talk up the ability of Afghanistan to survive the departure of its troops.

But NATO's rush to get out of a "quagmire" in Afghanistan risks the collapse of the state and strategic failure for the Western alliance in its decade-long war, former senior EU adviser on Afghanistan Barbara Stapleton warned in a report ahead of the summit.

Afghan President Hamid Karzai is in Chicago armed with a demand for $4.1 billion (3.2 billion euros) a year to fund his security forces after the pullout, amid fears the country could descend into a new civil war.

In return for the funding, Afghanistan will commit to preserving gains in respect of democracy and human rights, and to being an ally of the international community in the fight against terrorism.

Efforts to broker peace have stalled, with the insurgents in March pulling out of preliminary talks with the US in Qatar, saying Washington had not fulfilled confidence-building pledges such as releasing five Taliban leaders from the US military prison in Guantanamo Bay.

And they have steadfastly rejected talks with Karzai's administration, describing it as a puppet of the Americans.