(CNN) -- Ugandan forces arrested several terror suspects Saturday and recovered explosives during an operation to foil an "imminent" terrorist attack in the capital of Kampala.

Security forces ratcheted up security in public places during the operation as the U.S. Embassy warned Americans there to stay indoors.

The terror plot was by the Somalia-based militant group Al-Shabaab, according to the embassy. It did not specify the targets.

However, local police said based on the explosives seized, the plot was a possible repeat of last September's attack on Nairobi's Westgate Mall in neighboring Kenya.

Security forces declined to release the identities or number of suspects arrested, but said they were of various nationalities.

Earlier this month, a U.S. airstrike killed Ahmed Godane, the terror group's leader in Somalia. The group has since installed a new leader and vowed to avenge Godane's death.

"We are continuing our engagement with Ugandan authorities as we seek to assess the scope of the disrupted Al-Shabaab terrorist plot and whether there are members of the cell still at large," the embassy said.

Ugandan troops are part of African Union forces battling the Somalia-based militants whose attacks have crossed into Uganda before.

Last year, unidentified gunmen attacked the Westgate shopping mall in Nairobi, resulting in the deaths of 67 people, including four of the attackers.

In 2010, the militants conducted suicide bombings in bars filled with patrons watching soccer in Kampala, killing more than 70 people.

U.S. officials have issued warnings to its citizens in Uganda before.

In July, it asked travelers to avoid Entebbe International Airport near Kampala. The embassy cited a "specific threat" involving an unknown terrorist group.

Ugandan authorities have increased security at key sites, including the Entebbe airport, the embassy said Saturday.

Entebbe is the only international airport in the nation.

CNN's Christabelle Fombu and journalist Samson Ntale contributed to this report