NAHRIN, Afghanistan -- Food, medicine, tents and other aid supplies began pouring into the quake-shattered northern Afghan region around Nahrin on Thursday after workers used explosives to clear roads leading to the stricken area.

Afghanistan observed a national day of mourning for the victims, although the death toll in Monday's powerful temblor was unclear. Officials said it was in the hundreds, not the thousands as originally feared.

A strong aftershock Wednesday sent boulders tumbling across mountain roads, temporarily blocking efforts to rush relief supplies to tens of thousands Afghans left homeless by a devastating quake this week. But aid workers said boulders blocking main routes had been blasted apart with explosives overnight and that the relief effort was now in full swing.

"Everything is moving along quite well," said Sherine Zaghow, an aid coordinator for the French relief agency ACTED.

"The roads have been cleared and distribution has begin."

The 6.1-magnitude quake struck nearly 80 villages in a mountainous region nine miles in radius, leaving 100,000 people either cut off from food supplies or homeless. The United Nations said the death toll, at 600 confirmed dead on Wednesday, was expected to reach 800-1,200.

By Afghan standards, aid reached the quake-stricken Hindu Kush region with remarkable speed -- assisted by U.S. forces in Afghanistan to battle Taliban and al-Qaida forces and international peacekeepers whose first job is maintaining security in the capital, Kabul.

"We're here, obviously, for a combat mission, but when this unfortunate accident happened, we were standing by with our coalition partners," said Maj. Leanne Smullen, who accompanied two U.S. Chinook helicopters from Bagram air base laden on Wednesday with U.N. medical supplies and tents. The crew also evacuated one injured person.

U.S. provisions

Three Chinooks landed in Nahrin early Thursday loaded with wheat, blankets, California dates, water, and Army rations. U.S. soldiers jumped out of the choppers and circled them as aid was unloaded, providing cover in case of attack.

"It's never too much to be too safe. It's very possible we could have al-Qaida or Taliban that we don't know about in the area," said Marine Capt. Steven O'Connor, a military spokesman.

A Russian mobile hospital unit was on its way from Tajikistan, Interfax news agency reported. The International Security Assistance Force in Kabul was to bring a mobile medical unit later in the day, along with four doctors and eight medics. Pakistan dispatched a C-130 transport plane to Afghanistan carrying tents, blankets and medicine.

Teams of physicians from Medecins Sans Frontieres, or Doctors Without Borders, were being sent to look for injured survivors unable to make their way to makeshift clinics in Nahrin.

Despite rough, poorly maintained roads and frequent truck breakdowns, 2,000 tents, 10,000 blankets and 1,000 tons of food reached Nahrin, 105 miles north of Kabul, a little more than a day after the quake, U.N. spokeswoman Stephanie Bunker said. Clothing, mattresses, cooking sets, medical supplies and surgical units also were on the way.

It took desperate aid workers a week to reach villagers after a 1998 quake in northern Afghanistan killed 5,000 people.

Still, the needs were greater than the supplies at hand Thursday. U.N. officials said they need 20,000 tents, 160,000 blankets and 10,000 mattresses.

While considerable aid had reached Nahrin, the staging area for distribution, some residents in the old part of the city, which was completely destroyed, said Thursday that no assistance had reached them.

Haji Habib, 38, who lost eight relatives -- all children -- in the earthquake, came to the relief center because surviving members of his family had almost no food.

"We don't have any food, we just have dried bread," Habib said. "Here there is sugar, bread, tents and blankets, everything, but they don't distribute it. Why?"

Aid distribution to some of the 42 outlying villages was only just gearing up after reconnaissance teams concluded aerial and ground surveys Wednesday.

A new landslide prevented aid workers from reaching Burka north of Nahrin, where aerial reconnaissance showed half of the homes in eight villages had been destroyed, leaving 800 families homeless. Road crews had just cleared the dirt mountain track to the remote region when the 5.4-magnitude jolt loosened more boulders Wednesday, said U.N. regional coordinator Fahrana Faruqi.

Aid workers were deciding Thursday how to reach the area -- by donkey or helicopter -- said Alejandro Chicheri, a World Food Program spokesman in Kabul.

Relief efforts may be hampered by minefields left over from 20 years of conflict, their threat multiplied by concerns that the mines had been shifted by the quake.

"You just need one mine to stop everything," Chicheri said.

The United Nations said it remained concerned about conditions in the Panjshir Valley, tucked deep inside the Hindu Kush mountains north of Kabul, where six villages with 3,000 people were completely destroyed, and Lakankhel, where aid workers estimate up to 70 percent of homes in seven villages were destroyed, affecting 935 families.

Residents have been digging by hand through the rubble, searching for mattresses, carpets and any household goods to establish camps away from the collapsed walls and roofs of their mud-brick houses. Clusters of freshly dug graves dotted the slopes around the old town.