Sudan is sending hundreds of troop reinforcements to the troubled Blue Nile region, state-linked media said on Thursday, after reports of clashes with rebels in a strategic border town.
Battalion 191 has arrived in the Blue Nile state capital Ed Damazin and two more battalions are expected, reported the Sudanese Media Centre which is close to the security apparatus.
It said the move aims to "improve the security in Blue Nile... to clean the state of rebels."
Witnesses also reported fighter planes and helicopters in the area.
Sources told AFP that there has been fighting in El Kurmuk, a border town about 240 kilometres (150 miles) south of Damazin.
"The reports that are coming consistently from that region are (of) fighting between SPLM-N and SAF," one source familiar with the situation said on Thursday.
"Kurmuk seems to be the hot-spot there," he said, referring to the Sudan People's Liberation Movement-North (SPLM-N) and the Sudanese Armed Forces (SAF).
Another source on Tuesday had reported "heavy fighting" in Kurmuk since the start of the week.
The war in Blue Nile has generally not been as intense as the one in South Kordofan state, where the SPLM-N is also fighting, making the battle around Kurmuk unusual.
The SPLM-N claimed last Sunday to have pushed into the town's southwest but since then have made virtually no comment except to claim fighting continues in the town.
Sudan's army spokesman Sawarmi Khaled Saad could not be reached for comment on Thursday.
Last Sunday, he denied the rebels were near the town and said their claim was a "fabrication" designed to damage army morale.
Sudan's government severely restricts access to Blue Nile and South Kordofan, where the SPLM-N took has been fighting government forces since 2011.
Khartoum accuses South Sudan of backing the SPLM-N but the South denies involvement.
Kurmuk, an important trading centre on the Ethiopian border, is the third-largest town in Blue Nile and has been in government hands since November 2011.
The report of troops arriving in Damazin came a day after the rebel's spokesman, Arnu Ngutulu Lodi, told AFP that Khartoum had sent reinforcements from the Popular Defence Force (PDF) to the Blue Nile state capital.
The PDF are a type of reserve force used frequently to support the SAF.
A Sudan analyst said fighting in Blue Nile and Kurmuk would be no surprise ahead of possible talks between the rebels and the government, as each side would want to present themselves as being in a strong position.
The United Nations and the African Union have for months called on the SPLM-N and Khartoum to reach a negotiated settlement.
Fighting in the two states has led to "truly appalling" conditions for civilians trapped in the region, UN humanitarian operations director John Ging said in January.
More than 200,000 people have fled as refugees to South Sudan and Ethiopia, the UN says.
An additional one million have been affected inside Blue Nile and South Kordofan, according to figures from the humanitarian wing of the rebels and data from the government's aid agency.