KABUL, Afghanistan (AP) – Medecins Sans Frontieres became the first major aid agency to quit Afghanistan since the fall of the Taliban, saying Wednesday that the government failed to act on evidence that local warlords were behind the murder of five of its staff.

The Nobel prize-winning medical relief group, also known as Doctors Without Borders, denounced the U.S. military’s use of aid to persuade Afghans to snitch on insurgents, saying it risked turning all relief workers into targets. It was also dismayed that Taliban rebels tried to claim responsibility for the June 2 attack on its staff.

“We feel that the framework for independent humanitarian action in Afghanistan at present has simply evaporated,” said Kenny Gluck, MSF’s director of operations. There is a “lack of respect for the safety of aid workers.”

The withdrawal of Medecins Sans Frontieres, which had 80 international volunteers and 1,400 Afghan staff in the country before the June attack, is the most dramatic example yet of how poor security more than two years after the fall of the Taliban is hampering the delivery of badly needed aid.

More than 30 aid workers have been killed in the country since March 2003, rendering much of the south and east off-limits.

On Wednesday, a bomb exploded in a mosque where Afghans were registering for coming elections, killing at least two people, officials said. Three rockets fired into Kabul overnight blew up an arms dump at an Afghan military base and narrowly missed the Chinese Embassy. No one was hurt.

President Hamid Karzai said he regretted MSF’s decision and insisted authorities were investigating the June attack.

The government is “fully committed to bringing to justice those responsible for murdering the MSF employees” and making the country safe for aid workers, a statement from his office said.

The assault on the MSF workers in northwestern Badghis, the deadliest yet on an international relief agency, raised fears that the north was also becoming too dangerous.

Badghis police say two men on a motorcycle stopped an MSF vehicle as it returned to the provincial capital Qala-e-Naw from a rural clinic. The three Europeans and two Afghans inside were shot dead.

A purported Taliban spokesman claimed responsibility, and accused the victims of working for American interests – a shock to MSF, which relies on neutrality to protect staff who venture into war zones.

But MSF officials said Wednesday that the Afghan interior minister had told them there was “credible evidence” that a former local security chief in Badghis had ordered the killing to protest his ouster.

That the official, who wasn’t identified, has been neither arrested nor denounced “sends a message that it is acceptable to kill aid workers,” Gluck told reporters. A spokesman for Interior Minister Ali Ahmad Jalali had no comment.

The aid group also called on the U.S. military to halt its expanding use of humanitarian work to win over skeptical Afghans.

U.S. and NATO troops are running a string of so-called Provincial Reconstruction Teams across the country, setting up clinics, digging wells and doing other work normally carried out by civilians.

The military apologized in May for distributing leaflets telling Afghans that they had to provide information on militants if they wanted assistance to continue.

Blurring the distinction “puts all aid workers in danger,” MSF secretary-general Marine Buissonniere said.

The U.S. military said the protests were misguided.

“We don’t put anyone in danger,” spokesman Maj. Jon Siepmann said. Many aid groups were working effectively alongside American troops, he said. Others “need to direct their concern towards the Taliban, towards al-Qaida. We do nothing here but help.”

MSF, which won the Nobel Peace Prize in 1999, has been working in Afghanistan for 24 years – through a decade of Soviet occupation, a brutal civil war and the rise and fall of the repressive Taliban. A French staffer was killed in 1990, but they have never withdrawn until now.

Gluck said staff providing health care and support to hospitals in 13 of the country’s 34 provinces wept and begged them not to pull out this time either. He said action by the government, the U.S. military – and even assurances from the Taliban – could help them to come back.

“There are still massive unmet medical needs,” he said. “We would be very anxious to return.”