Sixteen people, including eight women and children, were killed when a Sudanese war plane bombed a village in the Nuba mountains, which for three weeks has been the scene of daily aerial attacks in a new war along the country's volatile north-south border.

Medical staff at a nearby clinic said the dead included a three-year-old child and an eight-month-old baby. They said another 32 people were wounded in Sunday's attack, many of them seriously.

A Nuba witness to the aftermath of the attack said a government Antonov plane had dropped five bombs on the market and water point of Kurchi, a village in a part of the mountains controlled by Nuba enrolled in the Sudan People's Liberation Army (SPLA) of South Sudan.

Fierce fighting erupted between the Nuba SPLA and Sudanese government troops and militias on 5 June. The Nuba leader, Abdel Aziz al-Hilu, told an African Union panel headed by the former South African president Thabo Mbeki that the trigger for the conflict was an order that his men be disarmed by 1 June.

According to a report of the meeting seen by the Guardian, Hilu told Mbeki that more than 3,000 people had disappeared – "either killed or their whereabouts are not known, either because they are Nuba or they are SPLA".

The Nuba mountains lie in South Kordofan state, on the southern edge of Sudan's Arabised north. Many Nuba fought alongside the southern SPLA in the 22-year civil war, seeking democracy, development and respect for the languages, religious observances and culture of the Nuba tribes.

The peace agreement that ended the civil war in 2005 and gave the SPLA a share in government in South Kordofan denied the Nuba self-determination and did not specify what would happen to the 30,000-strong Nuba rebel army in the event of South Sudan voting for independence.

Senior Sudanese officers have told the African Union panel that Khartoum's air campaign is aimed at preventing the SPLA in South Sudan resupplying the Nuba.

Antonovs and Chinese-made MIG-29s have bombed Kauda, east of Kurchi, on four occasions, destroying an airstrip where Khartoum claims weapons have been flown in from the south.

Kurchi, a village in the foothills of the mountains, has no airstrip. It is a market town of about 400 homes and lies on the main road between government-controlled Kadugli, the state capital, and SPLA-controlled Kauda.

The UN peacekeeping mission in South Kordofan, UNMIS, is under orders from the Sudanese government to withdraw from the state by 9 July, the day South Sudan officially declares independence. The mission's reports for Sunday 26 June make no mention of any military activity.

A senior UN official said the mission was already "deaf and blind" in South Kordofan as a result of increasing belligerence towards it by Sudanese troops, police and militias.

In one of the most serious incidents to date, on 17 June, an UN patrol was detained by government troops and subjected to a mock firing squad in army headquarters in Kadugli. A UN report seen by the Guardian said the peacekeepers "were lined up and a SAF [Sudan Armed Forces] officer cocked his AK-47 and pointed it at them … They were told that UNMIS must 'leave South Kordofan, or we will kill you if you come back here'."