BANGKOK, Thailand (AP) _ Thousands of Khmer Rouge refugees living on the Thai-Cambodian border have fled heavy artillery attacks and entered a U.N.- controlled camp, relief officials said Monday.

In the past week, about 10,000 Khmer Rouge refugees have moved to the new Site K camp on Thailand's eastern frontier southwest of Bangkok, to join about 3,000 others who have lived there since June, said a relief official, who asked not to be identified.

Officials said they believe the new arrivals have come from Phum Thmei, one of many military camps under Khmer Rouge control along the Thai-Cambodian border. Phum Thmei has reportedly suffered heavy shelling from Cambodia, which is backed by Vietnamese forces.

Last week, relief officials said they were encouraged by what appeared to be a gradual improvement in recent months in the relationship between Khmer Rouge and international humanitarian organizations.

Diplomats, relief workers and international human rights agencies have accused the Khmer Rouge of human rights abuses against the civilian population under their control.

Some officials speculate that by allowing the refugees to move into U.N.-assisted areas, the Khmer Rouge may be trying to present a better image in advance of an international conference on Cambodia in Paris next month.

The Vietnamese government has promised to pull its troops out by the end of September and the conference is expected to discuss formation of an interim Cambodian government.

The Khmer Rouge killed hundreds of thousands of people during its 3 1/2 -year rule after 1975. They have fought a guerrilla war from bases along the Thai frontier since being ousted by the Vietnamese invasion of Cambodia in 1978.

Relief workers say that 50,000 Khmer Rouge civilians live in camps supervised by the U.N. Border Relief Operation. But the number living in secret military bases outside U.N. control could be twice that large, they said.

Farther north from Phum Thmei, the population of another Khmer Rouge refugee camp along the border at O'trao has swollen to over 10,000 due to new arrivals from military camps, relief officials said.

Khmer Rouge officials have permitted medical teams to vaccinate 8,000 people in two military camps near the U.N.-administered Site 8 camp, they said.

In mid-April about 700 Cambodians left the secretive Khmer Rouge camp of Kaiche after it was heavily shelled and traveled a few miles to Sok Sann camp, run by the non-communist guerrillas of the Khmer People's National Liberation Front.