A suicide bomber targeting an army recruiting center in northern Afghanistan killed at least 37 people Monday afternoon, Afghan authorities said.

It was the latest indication that the Taliban is increasingly relying on mass casualty attacks to destabilize the government.

At least four children who were playing outside the Afghan National Army base in Kunduz province were killed in the blast, authorities said. Nearly 40 people were wounded, most of them prospective recruits, provincial officials said.

“There is no safety in Kunduz,” the provincial council chief, Mahbobullah Mahbob, said Monday night. “I am really afraid that one day I, too, will get killed.”

The bombing, one of the deadliest here in recent months, came four days after the provincial police chief was killed in a suicide bombing.

The Taliban asserted responsibly for the Monday bombing in a text message sent to journalists. The group also took responsibility for killing the province’s police chief, Abdur Rahman Sayed Khali.

Western diplomats and U.S. military officials say the recent attacks show that the insurgent group, having lost key strongholds in the past few months, is resorting to spectacular attacks to counter the notion that it is on the defensive.

Most of the recent attacks attributed to the Taliban have targeted Afghan security forces, often when they are around civilians.

The U.N. envoy in Afghanistan, Staffan de Mistura, said the Taliban appears less concerned than ever about killing civilians.

De Mistura said he reached that conclusion in recent weeks as the United Nations was finalizing its annual report on civilian casualties in Afghanistan. U.N. officials reached out to Taliban leaders this year to offer to let them review a draft of the report and rebut any of its findings, the envoy said in a recent interview.

The report, which was issued last week, showed that the Taliban and other insurgent groups were responsible for at least 75 percent of the 2,777 conflict-related civilian deaths last year.

De Mistura said U.N. officials assumed that the Taliban would respond and rebut the report’s findings because the group’s leaders had asked the organization last year for that opportunity.

“I thought they had a vested interest in doing that,” de Mistura said. But the Taliban did not respond to the invitation, he said. “My sad assumption is that they have decided that at this moment the priority is to create horror and terror even at the expense of public support,” the envoy said.

He called the latest bloodshed a “horror surge,” unleashed in response to the U.S. troop buildup.

U.S. military officials say the Taliban is likely to step up attacks this spring to undermine NATO’s plan to start transferring responsibility for security to Afghan forces in the summer.

As NATO roots out Taliban cells from strongholds in the south, the group has begun carrying out more attacks in the north and east.

“It’s them projecting their power in areas they don’t control,” a U.S. military intelligence official said Monday, speaking on the condition of anonymity to discuss intelligence assessments.

The official said the Taliban has warned Afghans that they should avoid being around security personnel.

“Don’t be around the Afghan government, don’t be around the puppet regime, don’t be around the coalition forces,” the official said, summarizing the message the group disseminates through night letters and other means. “If you are and you get hurt, you don’t have the right to complain.”

President Hamid Karzai’s office issued a statement condemning the Monday attack.

Karzai called the bombing a “serious crime and an unforgivable act of terror against those who wanted to join [the] army ranks to protect their nation.”

The Taliban’s influence has oscillated in Kunduz in recent years. Western officials in the province say the group no longer controls significant areas, but the province is among the places where the Taliban is attempting to make a comeback this year.

Mohammad Omar, who was the province’s governor at the time, was killed in October in a suicide bombing at a mosque.

Special correspondent Javed Hamdard contributed to this report.