Bosh Shag Omar, a local commander with the rebel Sudan Liberation Army (SLA), told Reuters by telephone the Russian-built Antonov aircraft bombed the village of Tadit, 40km south of the North Darfur capital al-Fashir, at 8am (0600 GMT) on Wednesday.
"The bombing killed 25 SLA men and many sheep and camels, a lot of houses are burned and civilians are injured," he said.
Aid workers at Zam Zam, a teeming camp south of al-Fashir for thousands of people displaced by violence, said they heard planes bombing south of the state capital between 8 and 9am local time (0600 and 0700 GMT).
"You could hear the explosions and see the smoke coming from the south. Everybody in the camp is very nervous," said one aid worker, who asked not to be identified.
Sudanese government and rebels
signed peace protocols in Abuja
Sulaiman Muhammad Jamus, the humanitarian coordinator for the Sudan Liberation Army, said earlier in the day that government forces had launched a counter-attack on Tuesday after the rebels entered the town of Tawilla.
"The government is now bombing one of our bases about 35km southwest of al-Fashir," said Jamus.
Jamus said the rebels had abandoned Tawilla after two days of heavy fighting with government forces. "Our troops are no longer in Tawilla. We are now back in our camps," he said.
Several weeks of skirmishes between government-backed militias and rebels around Tawilla erupted into heavy fighting when about 100 rebels stormed into the transit town early on Monday.
The United Nations has condemned the fresh fighting, which comes two weeks after both government and rebels signed peace protocols in the Nigerian capital Abuja.
"We don't care if the ceasefire collapses. We are ready to fight the government anywhere," Jamus told Reuters by satellite phone from an undisclosed location in the desert.
Some 30 Sudanese policemen
were killed on Monday
The fighting is the latest upsurge of violence in Darfur, where 22 months of conflict have driven some 1.6 million people from their homes, creating what the UN calls the world's worst humanitarian crisis.
Tawilla is an important trade and communications link to the remote west of Darfur, about 60km west of al-Fashir.
The government says that at least 30 policemen were killed in Monday's rebel attack, but has so far denied any bombing.
It is unknown how many people have been killed or injured in the fighting.
In Cairo, the rebel Sudan Liberation Movement on Wednesday denied the killing of policemen in Darfur that led to the declaration of a state of emergency, instead blaming Khartoum for the deaths.
"The SLM denies that its army launched attacks on (government) positions in the state of north Darfur and affirms that information provided by Khartoum is totally erroneous," a statement said.
"We don't care if the ceasefire collapses. We are ready to fight the government anywhere"
Sulaiman Muhammad Jamous,
Sudan Liberation Army
State Governor Osman Yusuf Kibir declared a state of emergency and a curfew across North Darfur on Monday in the wake of "a grave military escalation by the rebels."
Kibir said rebels of the SLM and the Justice and Equality Movement had violated a ceasefire 19 times in less than two weeks, despite signing a security protocol in Abuja on 9 November.
Both sides in the 21-month-old Darfur conflict have repeatedly accused the other of violating the ceasefire.