KABUL, Afghanistan – May was the deadliest month for Afghan civilians since the United Nations started tracking deaths in 2007, according to a report released Saturday.

Meanwhile, bombs killed 21 people nationwide Saturday — including a family on a religious pilgrimage and a child lured by a suicide attacker pushing an ice cream cart.

Violence has been on the rise as the Taliban and other insurgents try to regain territory lost in the fall and winter to the U.S.-led coalition in southern Afghanistan. The insurgents have stepped up suicide attacks and bombings that are more likely to affect civilians.

Fighting always picks up in the spring after the opium poppy crop is harvested in the south and the snow melts elsewhere in the mountainous country, allowing insurgents to move more freely. But attacks have intensified as militants try to undermine confidence in the Afghan government, which wants to show it is ready to take over security as the United States begins to withdraw some forces.

“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. Parties to the conflict must increase their efforts to protect civilians now,” said Georgette Gagnon, director of human rights for the U.N. mission in Afghanistan.

The U.N. said insurgents were responsible for 82 percent of the 368 civilians killed last month, with homemade bombs the leading cause of death. The international alliance and Afghan security forces were to blame for 12 percent of the deaths, according to the report.

NATO airstrikes, a cause of tension between the Afghan government and the alliance, were behind 3 percent of civilian deaths, the report found.

Despite those findings, much of the public anger over civilian casualties has focused on the international force.

Last month, President Hamid Karzai ordered the alliance to stop bombing homes after an airstrike accidentally killed a group of children and women in southern Helmand province. Coalition commanders apologized, saying the airstrike was launched when a gunbattle broke out after an insurgent attack on a patrol in the district killed a U.S. Marine.

But the incident and Karzai’s reaction has severely strained relations with the coalition and further complicated an already difficult relationship with the United States as President Obama prepares for a July troop drawdown in the increasingly unpopular war. In a videoconference with Karzai on Wednesday, Obama expressed his sorrow over recent civilian casualties in Afghanistan caused by coalition airstrikes.