Uganda feels "gutted" and "betrayed" by a UN panel of experts' leaked report which alleges that the country supports M23 rebels fighting the Democratic Republic of Congo government, foreign affairs state minister Okello Oryem has said.

He also reiterated that the UPDF will withdraw from the peacekeeping mission in Somalia if the UN Security Council adopts the report with the allegations in a Monday session.

"If the UN upholds the report and condemns Uganda, we shall withdraw. If they don't adopt the report and exonerate Uganda, we shall stay," Oryem said on Sunday.

He observed that Uganda had not softened its stance as articulated by the Prime Minister, Amama Mbabazi, in his address to Parliament a fortnight ago.

"On one hand they say we are thugs and on the other they say we are doing a good job. They cannot claim that the UPDF is a professional army, doing a fantastic job in Somalia and in the same breath say they are thugs promoting war in Congo by supporting M23 rebels. You choose either of that because the UPDF in Somalia is the same UPDF in Uganda," Oryem said.

The UPDF soldiers account for more than a third of the 17,600 UN-mandated African Union peacekeeping Mission (AMISOM) battling al-Qaeda-linked al-Shabaab militants in Somalia.

Uganda's threat to withdraw comes at a time when AMISOM and the Somali government forces have driven the extremists out of the capital Mogadishu and several key ports and towns in Somalia.

It is feared that a sudden reduction in troop numbers would undo the security and political gains that recently allowed the first parliamentary and presidential elections since 1991.