Ugandan forces arrested several terror suspects and recovered explosives in an operation to foil an "imminent" terrorist attack on the city of Kampala, the country's police said Saturday.

Meanwhile, the U.S. Embassy warned Americans there to stay indoors. The country's security forces have ratcheted up security in all public places, vowing to "effectively defeat whoever tried to endanger the lives and property of the people of Uganda," according to a police press statement.

The foiled terror plot was by the Somalia-based militant group Al-Shabaab, the U.S. Embassy in Kampala said; it did not specify the targets. However, local police said that based on the type of explosives seized, they saw this attack plot as a possible repeat of last September's attack on Nairobi's Westgate Mall and were particularly concerned about crowded areas.

Security forces were still searching for more suspects and and have 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. Information on the threat came from Ugandan police, it said.

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)