Indonesia has thwarted a bid by Daesh-linked terrorists to stage a series of bombings when it announces official election results this month, authorities said.

Anti-terrorism police have shot dead one terrorist and detained six suspected of planning attacks on officers in Sumatra and near the capital Jakarta with firearms or suicide bombings under the cover of rallies tied to recent elections, a police spokesman said.

The suspects were detained after weekend raids in Bekasi in West Java and one died after being shot when he threw a bomb at police, national police spokesman Dedi Prasetyo said.

"They were planning to take police firearms and use them to commit terrorism, whether by becoming suicide bombers or performing other attacks that could be fatal for protesters," Prasetyo said, adding that explosives had also been seized.

The roundup comes after Daesh-inspired Easter suicide bombings killed 257 in Sri Lanka, and as Indonesia marks the anniversary of its worst terror attack in years, which saw a dozen killed at churches targeted by suicide bombers last May.

Authorities said the arrested militants were members of Jemaah Anshurat Daulah (JAD), a local terrorist group that has pledged allegiance to Daesh and was blamed for last year's church bombings.

The group planned to set off bombs at various locations when the world's biggest Muslim majority nation releases election results on May 22.

There are concerns about street demonstrations after presidential challenger Prabowo Subianto, a retired military general, warned protests could erupt over his allegations of massive electoral fraud.

Subianto has vowed to challenge the official results if they confirm that his rival, President Joko Widodo, won a second term.

National police spokesman Dedi Prasetyo said the terror cell planned to target police stations and take advantage of any chaos before or after the poll results are confirmed.

"They have two goals -- the first is to target police officers and the second is to exploit election momentum," he said.

Last year, two families carried out bombings at churches in Indonesia's second-biggest city Surabaya, killing a dozen people and children of the attackers, including two young girls. It was Indonesia's worst terror attack in years.

Since the 2002 Bali bombings, which killed over 200 people including scores of tourists, Indonesia has seen a string of deadly attacks that have tested its long-held reputation for religious tolerance.

In March, police said they had uncovered a huge stash of explosives linked to a JAD terror suspect whose wife blew up herself and a child following a dramatic standoff at their home.

The discovery of some 300 kilograms (660 pounds) of assembled explosives and bomb-making materials had raised fears that a major attack was being planned ahead of last month's elections.