GUNMEN FROM AN Arab tribe fired on four UN helicopters taking off from a disputed north-south Sudan border town, an official said today, while Sudan’s president gave northern troops a “green light” to attack southern forces if provoked.

UN spokeswoman Hua Jiang said the helicopters were fired on as they took off from Abyei town late Tuesday. She said about 14 rounds were fired from positions close to the UN compound. No helicopters were hit.

Both Sudan’s north and south claim Abyei, a fertile region that is located near several oil fields. Northern tanks and soldiers rolled into the disputed region Saturday following an attack on a northern army convoy last week.

Southern Sudan voted in January to secede from the north in July, but the north’s occupation of Abyei has greatly strained north-south relations. The two regions fought a two-decade-plus civil war that claimed two million lives, and fears are rising Abyei could send the sides back to war.

Sudanese President Omar al-Bashir gave his army a green light to attack southern forces without seeking permission from Khartoum if they feel provoked, according to a statement carried Wednesday by Sudan’s state news agency.

Since an attack last Thursday by southern troops on northern and UN forces, northern troops have moved south into Abyei, sending thousands of civilians fleeing. Northern aircraft are reported to have made bombing runs in the region, and the UN said that gunmen set homes ablaze and looted in Abyei town.

The south has called the move into Abyei an act of war but has not yet responded with force.

Al-Bashir said the US is applying a double standard between the government of Sudan and the government of Southern Sudan by ignoring the fact that southern troops attacked northern troops last week, the event that set off the latest crisis.

The US has been looking to reward Sudan for a successful southern independence process by removing Sudan from the list of state sponsors of terror, by helping it get debt relief and by normalizing relations.

Princeton Lyman, President Barack Obama’s Special Envoy to Sudan, said this week that those rewards are in jeopardy if the independence process is not completed. But al-Bashir indicated he was no longer interested in the incentives.

“We no longer fear the American stick nor do we desire its carrots,” al-Bashir was quoted as saying.

The south’s secession vote was promised in a 2005 peace deal that ended the north-south civil war. The conflict over Abyei could scuttle the Comprehensive Peace Agreement that promised the January independence referendum and the July 9 independence date.

A referendum on Abyei’s future was supposed to have been held simultaneously, but the two sides could not agree on who was eligible to vote, and Abyei’s referendum wasn’t held. The black African tribe of the Ngok Dinka, which is allied with the south, and the Arab tribe of Misseriya, which is allied with the north, both claim the area.

Jiang, the UN spokesman, said that Misseriya tribesmen are moving south into Abyei town, though she did not know how many.

- AP