Uganda said on Friday that its troops sent this week into eastern Democratic Republic of Congo would stay as long as needed to defeat Islamist militants, with the progress of the mission to be evaluated after two months.

Uganda and Congo launched a joint operation this week, but have so far shared few details about its size or expected duration, even as some voiced alarm about the presence of Ugandan troops on Congolese soil.

At least 1,700 Ugandan soldiers have so far crossed into eastern Congo to join Congolese forces battling the Allied Democratic Forces (ADF), an armed group aligned with Islamic State, two security sources and local media said on Friday.

The Ugandan defense ministry did not confirm how many troops had been deployed, but said infantry, artillery, armored and special forces would be in Congo under Operation Shujja, which means hero in Swahili.

In its first clear indication of the duration of the planned operation, Uganda's Ministry of Defense said in a statement that the operation would be reviewed after two months to gauge its progress against the ADF.

"The duration of this operation will be determined by the military-strategic end-state... to defeat the rebels and defeat their will to fight," Major General Kayanja Muhanga said in a video posted to Twitter.

The campaign will target four ADF camps: Yayuwa, Tondoli, Beni One and Beni Two, he said.

Joint forces have already conducted search operations in the wake of air and artillery strikes against suspected ADF bases in the forests of eastern Congo earlier this week, according to both countries' military.

Hundreds of Ugandan soldiers and dozens of armored vehicles have been seen crossing the border at Nobili since the offensive started on Nov 30. The two security sources with knowledge of the mission said another 300 Ugandan troops were expected to arrive imminently.

The scale of the deployment suggests it is the largest foreign intervention in Congo in over a decade, apart from a U.N. peacekeeping operation, said Pierre Boisselet from Kivu Security Tracker, which monitors unrest in the region.

Congo's government spokesperson did not immediately respond to a request for comment about the number of Ugandan soldiers in Congo.

"Deployments are still going on, so I can't say whether we have a battalion yet, or brigade or whatever," Uganda's army spokesperson Flavia Byekwaso told Reuters.

Uganda blamed the ADF for a triple suicide bombing in its capital Kampala on Nov. 16, which killed seven people, including the bombers.

The ADF began as an uprising in Uganda but has been based in Congo since the late 1990s. It pledged allegiance to Islamic State in mid-2019 and is accused of killing hundreds of villagers in frequent raids over the past two years.

Islamic State has claimed responsibility for some of the ADF's violence, including the recent bombings in Uganda, but United Nations researchers have found no evidence Islamic State exerts command and control over ADF operations.

(Reuters)

Democratic Republic of Congo soldiers rest next to a road after Allied Democratic Forces rebels attacked area around Mukoko village, North Kivu province of Democratic Republic of Congo. (Reuters)

Uganda says troops to stay in Congo as long as needed to defeat ADF