By Simon Apiku

KHARTOUM, Sept 11 (Reuters) - Heavily armed police raided premises of Sudan's junior coalition government partner on Tuesday, threatening a partnership created under a peace deal that ended 20 years of north-south war, the party said.

The Sudan People's Liberation Movement (SPLM) said the raids, which targeted three of its offices in the capital, followed a campaign and slanderous attacks against senior SPLM officials in the national media.

"We are really fed up of what's going on," Yassir Arman, deputy secretary general of the SPLM, told Reuters.

The interior ministry was not immediately available for comment.

The SPLM signed a peace agreement with the northern National Congress Party (NCP) in 2005, ending more than two decades of north-south conflict that left some two million people dead and forced four million to flee from their homes.

It resulted in the SPLM joining the government.

SPLM sources said that heavily armed police and security forces, backed by armored personnel carriers, stormed their offices in Khartoum North, Dem, and Mogran, vandalising property, and in one case, breaking down a door.

PORTRAIT OF GARANG

One source said a portrait of the founder of SPLM leader John Garang, who died in a helicopter crash two years ago, was also destroyed.

"It is uncalled for. It is going to impact negatively on the relationship between the National Congress and the SPLM," said Arman. The SPLM said the police searched the offices.

Arman said as an important member of the ruling coalition, the SPLM leadership should have at least been informed if there was a legitimate reason to search the party's offices.

"Obviously out of courtesy they were supposed to inform the leadership of the SPLM and we were supposed to be there," he said. "But they came and searched us like criminals. That is unfortunate," the SPLM deputy secretary general said.

The incident came just three days after rumors about the death of Salva Kiir, the leader of the SPLM and president of the semi-autonomous government, which created tensions in Khartoum that only eased after Kiir appeared on state television to dispel the reports.

But those tense moments reminded many of the bloody confrontations between southern and northern Sudanese in the wake of Garang's death in 2005 in which more than 100 people were killed in the capital.