Indonesian police say they have seized a large quantity of explosives and bomb making material being smuggled from Malaysia.
Police have been on high alert since this month's Bali attack
Three women and a man have been arrested, said the police chief of East Kalimantan, Djoshua Sitompul.
Mr Sitompul told the BBC that most of the 175kg of explosives seized had already been made into bombs which were ready to detonate.
Police have been on high alert since a deadly attack in Bali on 1 October.
Mr Sitompul said the suspects came from Pare Pare in Sulawesi, Indonesia, and had been to Tawau in eastern Malaysia. They were seized in Nunukan, in the Indonesian province of East Kalimantan.
"We are still investigating this case to determine whether the four suspects have links with previous bombings including Bali," he said.
He said four other suspects escaped and are still at large.
As well as the explosives, police also found 1000m of explosives fuse and 900 detonators.
Mr Sitompul said that police were also searching for a man he identified only by his initials AM, whom he described as "the owner of those explosive materials", according to the Associated Press.
Indonesian police are still searching for the masterminds of a suicide attack on the holiday island of Bali earlier this month which killed 20 people.
They have taken in several people for questioning but have yet to press charges against anyone.