JAKARTA (Reuters) - Indonesian police said on Tuesday that three people had been arrested over a suspected plot to carry out a suicide bomb attack in an undisclosed location outside the most populous island of Java.

Two men were arrested in the Central Java city of Solo on Sunday on suspicion they made explosives to be carried by a female accomplice, said Martinus Sitompul, a spokesman for the national police.

A suspected female suicide bomber had been arrested in Purworejo, also in Central Java, last Thursday, he said.

“The group was planning to carry out an attack outside Java,” Sitompul said. He declined to elaborate and said police would hold a news briefing later this week.

The three were linked to a group police arrested earlier this month for planning an attack at the changing of the guard at Jakarta’s presidential palace, he added.

In both cases, police suspect the groups planned to use a female suicide bomber, a new tactic for attacks in Indonesia.

The suspects held over the planned Jakarta attack had been communicating with and received money from Bahrun Naim, an Indonesian militant known to be fighting with Islamic State in Syria, police have said.

Indonesian police are currently interrogating 14 suspects related to the planned Jakarta bombing and the plot outside Java, Sitompul said.

Security is usually stepped up in Indonesia at this time of year, following attacks in previous years during Christmas and New Year celebrations.

Earlier on Tuesday, a bomb squad on the Indonesian island of Bali detonated an unattended backpack in the city of Ubud with a sign saying “bomb”. Bali police spokesman Made Sudana said there was no bomb threat and it contained fireworks, adding the backpack belonged to a Dutch man who had lost it.

Bali has suffered two major attacks including nightclub bombings in 2002 that killed 202 people, and suicide attacks in 2005 that killed 20.