Democratic Republic of Congo President Joseph Kabila's chief adviser was killed and his finance minister seriously injured in an airplane crash near the eastern town of Bukavu Sunday, officials said.

The accident, the latest in a country with one of the world's worst air safety records, comes as Kabila braces for negotiations to form a new coalition government after his disputed victory in a chaotic election in November.

Adviser Augustin Katumba Mwanke, 58, was regarded by many as the power behind the throne, according to a leaked 2009 U.S. diplomatic cable. He was a former governor of the copper-rich province of Katanga and retained major influence in the country's minerals sector.

Summing up Katumba's power, one Congolese senator said on condition of anonymity: If you wanted to negotiate business and Kabila said 'yes', that was 50 percent, but if Katumba said 'yes', that was 100 percent.

Government spokesman Lambert Mende said the plane's pilot had also died in the crash.

He confirmed Katumba's death, saying: It's a very big loss, he was considered a pillar of the presidential majority.

Lambert said Finance Minister Matata Ponyo Mapon and roving ambassador Antoine Ghonda were heavily wounded in the crash and Marcellin Cishambo Rohuya, governor of the local South Kivu province, was lightly injured.

No official death toll was immediately available and details of the crash were patchy. A United Nations spokesman said the small plane appeared to have overshot the runway.

I don't have the number (of passengers) but according to our people in South Kivu the pilot landed in the middle of the strip, and went over the end, said Alexandre Essome, spokesman for the U.N. mission MONUSCO in the eastern town of Goma, from where the plane had taken off.

Ponyo is seen as an effective operator despite snags over the recent introduction of VAT tax which saw confusion and a sharp jump in inflation. His goal was to bring annual inflation down to 9 percent in 2012 from 15 percent last year.

BAD PRESS

The publicity-shy Katumba was a more controversial figure.

He was seen as someone who pushed for power to be held by an inner circle around Kabila and his demise is an unpredictable new element in forthcoming coalition talks with opposition parties who rejected Kabila's poll victory as fraudulent.

It could also herald major changes in the way Congo handles it huge resources, ranging from copper to gold, oil, diamonds and tin, and in the way it conducts business with international donors and investors.

The 2009 diplomatic cable released by WikiLeaks noted that Katumba had been blamed within the government for bad press surrounding a $9 billion mines-for-infrastructure deal with China. The deal, criticised by the International Monetary Fund and others for selling the country's assets short, was eventually revised down to $6 billion in volume.

He had earlier been named in a 2002 report by the U.N. monitoring Group of Experts as being part of an organization that illegally seized control of billions of dollars' worth of state mining assets. He was briefly suspended from government following the report.

Kabila has been in power since a 2006 vote that drew a line under years of war and chaos in the central African country. But progress in developing its wealth has been slow and critics say corruption remains rampant.

Kabila was inaugurated for a new term in December despite broad misgivings over the November 28 poll, which was marred by bad organization and evidence of irregularities that sparked protests. Human Rights Watch said at least 24 people have been killed by security forces since results were announced.

Kabila's ruling party has also emerged in the lead from parliamentary elections held on the same day, but it won fewer seats than it had before, complicating the president's task of forming a solid coalition government.

(Additional reporting by Bienvenu-Marie Bakumanya in Kinshasa and Mark John in Dakar; Writing by Mark John; Editing by Ben Harding and Alessandra Rizzo)