Khartoum – Satellite images taken on Friday showed northern Sudanese military vehicles including heavy transports and artillery massing in the capital of the conflict-stricken Southern Kordofan state, a monitor said.
Fighting between the northern military and southern-aligned groups has spread across the key north-run oil state since 5 June. Tens of thousands have fled the violence, according to the United Nations.
The clashes have also raised tensions at a sensitive time in Sudan, with the south less than three weeks away from becoming an independent country following a January referendum.
"New imagery…confirms that the Sudan Armed Forces, or SAF, control the town of Kadugli in Sudan's tense border region of South Kordofan, and that thousands of civilians have been displaced," the Satellite Sentinel Project (SSP) said in a report.
The images "show a massing of SAF artillery, light vehicles, and heavy transports of the kinds used to carry tanks, troops, and munitions."
Set up last year by Hollywood actor George Clooney and other activists, the SSP says it seeks to head off renewed fighting and atrocities in Sudan by publishing commercial satellite images collated and analyzed with the help of a UN agency.
A spokesman for the northern military was not immediately available to comment on the report. It has previously said its forces were fighting to end an armed rebellion in the state.
Southern Kordofan – the main oil-producing state that will be left in the north after the south secedes on 9 July – is home to thousands of fighters who fought against Khartoum during the last civil war, many of them from the Nuba mountains region.
Officials with the south's dominant Sudan People's Liberation Movement have said clashes started when the north tried to disarm fighters there.
Northern officials have blamed the southern-aligned groups for provoking the fighting after an official from the north's ruling National Congress Party was named winner of a state gubernatorial election last month.
The south's independence vote was promised in a 2005 peace deal that ended decades of civil war. That conflict claimed some two million lives.