Anti terror policemen stand beside goods seized from a house of suspected Islamist militants in Bandung, West Java province, Indonesia August 15, 2017 in this photo taken by Antara Foto. Antara Foto/Agus Bebeng via REUTERS.

JAKARTA (Reuters) - Indonesian police on Tuesday arrested five suspected Islamist militants and seized chemicals near the capital, Jakarta, that they said were being used to make bombs for attacks on the presidential palace at the end of August.

Two of the five, a husband and wife, had been deported from Hong Kong for allegedly spreading radical ideology and the group had studied bomb-making techniques through a website run by an Indonesian believed to be fighting with Islamic State in Syria, police said.

Indonesia, the world’s most populous Muslim-majority nation, has seen a series of small-scale attacks inspired by Islamic State, but most have been amateurishly planned and executed, using basic homemade weapons that have caused few deaths and minimal damage.

Police have been concerned about suspected militants getting more sophisticated after twin pressure cooker bombs killed three police at a Jakarta bus station in May.

“This is perhaps the first time such a method has been used in West Java, involving very dangerous chemicals,” said provincial police spokesman Yusri Yunus, adding that several stores had declined to sell the chemicals to the suspects.

Yunus did not elaborate on the chemicals or the plan to attack the presidential palace. West Java is just to the east of Jakarta.

Counter-terrorism police who found the chemicals in a raid on a house in Bandung, 120 km (70 miles) southeast of Jakarta, said they experienced a burning sensation and redness on their skin when they entered the house.