Kabul, Afghanistan (CNN) -- The number of civilians killed in attacks and other war-related violence hit 368 in May, making it the deadliest month for Afghans since 2007, the United Nations said Saturday.
The news came as Afghan authorities said three attacks in separate parts of the country killed at least 24 people, including 10 children, raising concern that civilians are increasingly being targeted in intense fighting since insurgents launched their so-called spring offensive.
"We are very concerned that civilian suffering will increase even more over the summer fighting season which historically brings the highest numbers of civilian casualties," Georgette Gagnon, the director of human rights for United Nations Assistance Mission in Afghanistan, said in a statement.
"Parties to the conflict must increase their efforts to protect civilians now."
The top coalition commander in Afghanistan has warned of a likely increase in high-profile attacks by insurgents looking to demonstrate their ability to strike.
In a letter to coalition forces last month, Army Gen. David Petraeus said the attacks may increase the risk of civilian casualties, and put Afghan and coalition forces in difficult situations.
Insurgents and other anti-government forces were responsible for 301 civilian casualties in May, according to the U.N. agency, which began recording Afghan civilian casualties in 2007.
Forty-five deaths were blamed on Afghan and NATO-lead forces, according to the U.N. agency
Twenty-two civilians were killed in crossfire between the two sides, it said.
Bomb blasts caused by improvised explosive devices were the leading killer of civilians in May, with 119 killed and 274 wounded in such attacks, the U.N. agency said.
May is also the deadliest month for international troops in Afghanistan this year. Fifty-seven service members were killed in May, according to a CNN count.
In the latest death, a service member was killed in an insurgent attack on Saturday in southern Afghanistan, said NATO's International Security Assistance Force. More than 20 international forces have died this month.
The wave of attacks on Saturday drew condemnation from Afghan President Hamid Karzai, the U.S. Embassy in Kabul, and ISAF.
"Innocent people woke up this morning looking forward to a day off with their families or went to work as policemen sworn to protect their fellow Afghans. They will not return home today, despicably killed at the hands of insurgents bent on preventing peace and stability sought by the vast majority of the Afghan people," said Rear Adm. Vic Beck, ISAF spokesman.
A roadside bomb blast Saturday killed 15 people, including eight children, in volatile Kandahar province in southern Afghanistan, the Ministry of Interior said.
The explosion in the south occurred when "a civilian vehicle hit a roadside mine" in the Lahore district of Kandahar province, the ministry said in a statement. Four people, including a woman, were wounded in the explosion, it said.
A mortar attack in the Laghman province killed six civilians, including two children, officials said.
Earlier, a suicide bomber detonated explosives outside a police station in the Khost province, killing three people, said Arif Pashton, a provincial council member.
There were conflicting reports about whether a child was among the dead in that explosion.
Pashton said all three killed were police officials, but Hedayetullah Hamidi, the acting chief at Khost hospital, said one of the fatalities was a child.
He said 23 people were wounded.
Conflicting casualty reports are not uncommon in the aftermath of an attack.
Among the dead, according to Pashton, is the commander of Khost's quick reaction police force -- a special operations unit.
CNN's Eve Bower, Chelsea J. Carter and Joe Sterling contributed to this report.