Ugandan security forces are on high alert after they said fighters from an Islamic State-linked group entered the country at the weekend.
The Allied Democratic Forces (ADF) militants are planning attacks in urban areas, places of worship, schools and public events, according to the army.
It urged the public to remain vigilant "to avoid being victims of ADF terror".
The ADF has been linked to a series of deadly attacks in Uganda, including targeting a school last June.
The group was originally formed in Uganda in the 1990s by people disgruntled with the government's treatment of Muslims. But after being routed by the army, the remnants fled across the border to the Democratic Republic of Congo.
In 2021, Uganda and DR Congo launched a joint offensive to drive the ADF out of their Congolese strongholds, but have so far failed to put an end to the group's attacks.
Uganda's President Yoweri Museveni has repeatedly said the operation has succeeded in killing a large number of ADF fighters, including some commanders.
But the ADF has been accused of continuing to carry out attacks including on a school in western Uganda in June last year, when dozens of pupils were killed. In October last year, the group was blamed after a honeymooning couple and a Ugandan tour guide were shot dead in a national park.
Uganda's deputy military spokesperson Col Deo Akiiki said in a statement released on Monday that a group of ADF militants crossed into Uganda from DR Congo on Saturday.
"This group is suspected to be under the command of a notorious ADF commander Ahamed Muhamood Hassan, aka Abu Waqas, a Tanzanian-born ADF bomb expert," the statement added.
The army urged the public to identify and report any suspicious individuals or packages as it "catches up with this group".