Uganda's threat to pull its troops out of Somalia in retaliation for allegations it backs rebel forces in war-ravaged Congo could dangerously weaken Somalia's fragile, Western-backed transitional federal government only weeks after it was installed.

Ugandan forces account for more than one-third of the 17,600-person United Nations-mandated peacekeeping force that recently drove al-Qaida-linked al-Shabaab insurgents out of their last key stronghold in Somalia.

If the Ugandans are withdrawn, al-Shabaab's prospects of regrouping and retaliating are greatly enhanced.

This could be accompanied by terrorist attacks against TFG allies like Kenya and Burundi and possibly even further afield in East Africa at a time when the long-neglected region is on the cusp of a major oil and natural gas boom.

Indeed, these events are linked to the seeming endless Congolese war and unrest in other parts of Central and East Africa.

The Kampala government has vigorously denied allegations leaked from an October report by U.N. experts that Uganda supports the M23 rebel group in the Democratic Republic of Congo led by renegade self-styled general Bosco Ntaganda.

The warlord, known as "The Terminator" for the atrocities attributed to his bloodthirsty fighters, has been indicted by the International Criminal Court for war crimes committed in the long war over the Congo's mineral riches that has drawn in a dozen other states over the years.

The government of Uganda's veteran leader, President Yoweri Museveni, hasn't ordered his military forces to quit Somalia but Ugandan Security Minister Wilson Mukasa says the decision to withdraw Ugandan troops from Somalia and other African hotspots is "irreversible."

Ugandan forces are also deployed in the DRC and maintain a presence in South Sudan.

Ugandan troops backed by U.S. Special Forces are leading the manhunt for fugitive Ugandan warlord Joseph Kony in the Central African Republic.

The Ugandans in Somalia are part of an African Union peacekeeping force known as Amisom. They played a leading role in a yearlong campaign against al-Shabaab, presumably participating at Washington's behest.

The Islamists had battled to topple the corruption-riddled TFG installed in Mogadishu, Somalia's capital, by U.S.-backed Ethiopian forces which toppled an Islamist coalition in December 2006.

Since Amisom, spearheaded by Kenyans, drove al-Shabaab out of the southern port of Kismayu, their last urban bastion, the Islamists reportedly have been reorganizing in preparation for a country-wide guerrilla campaign.

They're also expected to ramp up terrorist attacks in Kenya and Uganda. On July 11, 2010, they killed 76 people in two bombings in Kampala, apparently in retaliation for Uganda's military presence in Somalia.

That attack was the first major terrorist operation involving al-Shabaab outside Somalia and there are fears the group will widen these attacks across East Africa.

Al-Qaida has long had a cell in the region. It was responsible for the near-simultaneous bombings of the U.S. embassies in Nairobi, Kenya's capital, and Dar-es-Salaam in Tanzania Aug. 7, 1998.

On Nov. 28, 2002, the al-Qaida cell carried out the suicide bombing of the Paradise Hotel in Mombasa, Kenya, killing three Israelis and 12 Kenyans.

At the same time, attackers fired two surface-to-air missiles at an Israeli jetliner with 271 people aboard shortly after take-off from Mombasa Airport. Both missiles missed.

Al-Qaida's leader in East Africa, Fazul Abdullah Mohammed, who masterminded these attacks, was killed in Mogadishu June 8, 2011.

If the Ugandans do quit Amisom in Somalia, al-Shabaab will score a significant gain without firing a shot. That could give it a boost when it needs it most, probably at the expense of the TFG and Amisom.

Somali Prime Minister Abdi Farah Shirdon Saaid says the TFG wants the Ugandans to stay, warning that their withdrawal "at a critical moment ... will be a challenge."

A major al-Shabaab comeback now could seriously weaken Amisom, imperil the new government elected only a few weeks ago and plunge Somalia into another round of fighting.

The United Nations has also accused Rwanda, the DRC's tiny eastern neighbor, of arming, funding and even commanding M23.

It's taken large areas of eastern Congo in the latest phase of a multination war that erupted in May 1996 and, but for a one-year halt, has dragged on since.

Both Uganda and Rwanda deny aiding the M23 rebels, a large well-equipped force of veteran jungle fighters, mercenaries and Congolese army deserters.