Africa's porous borders mean it will be difficult to prevent attacks elsewhere in the region like Sunday's twin bombings in Kampala that killed 73 people, U.S. ambassador to Uganda Jerry Lanier said on Wednesday.
The deadly explosions in Uganda were claimed by the al-Shabab group, which western authorities say is linked to al-Qaida. If confirmed, it would be the first time the Somali rebels had carried out a long-standing threat to attack their enemies in other countries.
"Suicide bombers are very difficult to stop in any country and we know that African borders tend to be more porous than other countries," Lanier told Reuters.
"The Ugandans, I'm sure, were taking measures they thought were adequate, but it is just very difficult to prevent these kinds of attacks," he said.
Lanier said it was "entirely possible" that other countries in the region threatened by al-Shabab, such as Burundi, Ethiopia and Kenya, could face similar attacks.
"It has awakened the region to the threat. Because of the multiple threats we've all heard in the past ... this gives some reality to that threat," he said.
The ambassador said Washington was prepared to step up its support for Uganda in the wake of the attacks, adding that more FBI agents would arrive on Wednesday and Thursday to join the three already helping the investigation.
"We will see what (Uganda's) needs are and go from that," he said, citing financial and logistical support as likely.
Lanier said the attacks may have been designed to scare off those countries in the region that have at times promised to increase their role in Somalia and join Uganda and Burundi in providing troops on the ground.
"It is perhaps what al-Shabab were seeking, to intimidate countries that might otherwise be a part of AMISOM (the African Union force in Somalia), who might want to participate with Uganda in the struggle against al Shabaab."
The troubled Horn of Africa nation has been brought to its knees by the three-year insurgency, as Islamist rebels have battled the U.N.-backed Somali government, which is supported by the 8,100-strong African Union force.
Last week, the regional bloc IGAD promised to send an extra 2,000 peacekeepers to help resist the insurgency in Somalia, where at least 21,000 people have died in the fighting and some 1.5 million have been driven from their homes.
Al-Shabab enforces its own strict interpretation of Islam, routinely banning sport, music and dancing.