Police on Tuesday arrested two terrorism suspects and said they were looking for three others.
They said the group was planning a major attack on a mall in Nairobi on Wednesday.
According to the Daily Nation the two were arrested at 3pm, moments after they picked a parcel at a courier office in Ngong Town.
Sources said undercover officers who had been waiting for hours opened the parcel and found a live bullet.
It also had a map of the shopping mall on Ngong Road, with instructions to call the sender of the parcel in Isiolo and confirm it had been received.
According to a source privy to the operation, the officers asked one of the suspects to make the call as they listened.
It is after the voice on the other end gave more orders that police confirmed that they were dealing with a serious security matter.
The orders were that the recipients of the parcel should travel to Eastleigh where they were to meet another man.
They were required to show him the bullet, after which he would give them 1,000 live rounds and 10 AK-47 rifles.
Police said they traced the signal of the caller at Embulbul, a few kilometres from Ngong Town.
A senior police officer who confirmed the operation said they were looking for three other people.
The covert operation was conducted in Eastleigh and Ngong by an elite unit without the knowledge or involvement of the local police.
Reports say the attack would take place on Wednesday and would be similar to the Westgate one in which more than 70 people died and hundreds of others injured.
DAILY NATION