AMMAN (Reuters) - Militants behind an attack on Jordanian police supported Islamic State and investigations had revealed plans for more attacks on security and civilian targets, Jordan’s interior minister said on Monday.

Jordanian police said on Saturday a homemade explosive device planted near a police van killed a policeman and injured six others the day before.

The police vehicle had been maintaining security near a music festival in the majority Christian town of Fuhais, near the capital Amman and 15 kilometers (about 10 miles) from the hillside city of Salt.

In a huge security operation, Jordanian forces laid siege to a building in a residential part of Salt on Saturday night in search of those responsible for the bomb attack.

After the suspected militants refused to heed calls to surrender, the security forces stormed the building in a shoot out that resulted in the death of three militants and four security personnel, police said.

Ten members of the security forces were also injured.

Interior Minister Sameer al-Mobaideen said the militants, who blew up part of the building when the security forces stormed it, did not belong to a specific group but subscribed to Islamic State ideology.

Militants from Islamic State and other radical jihadist groups have long targeted U.S.-allied Jordan and dozens of militants are serving long prison terms.

“There were plots to wage a series of terror attacks that sought security points and popular gatherings. We know the targets but we won’t tell them so people won’t get terrified,” Mobaideen said.

King Abdullah, a Middle East ally of Western powers against Islamist militancy who has also safeguarded Jordan’s peace treaty with Israel, warned on Saturday the perpetrators of the attack would pay dearly.

SECRET INVESTIGATIONS

The monarch has been among the most vocal leaders in the region in warning of threats posed by radical groups.

The group were all Jordanian and there were no signs so far they had foreign links, Mobaideen said, refusing to give names of suspects. “The investigations are secret and ongoing,” he told a news conference

Alongside automatic weapons in the suspect’s possession, the authorities found a location where chemical ingredients for manufacturing explosives were buried, Mobaideen added.

General Hussein Hawatmeh, head of Jordan’ Gendarmerie, said the militant cell was recently set up and there were indications its members had embraced radical ideology.

“What is dangerous is that these new recruits are more impulsive than those with experience in executing operations that harm Jordan’s security,” Hawatmeh told reporters.

Jordan has been relatively unscathed by the uprisings, civil wars and Islamist militancy that have swept the Middle East since 2011.

But there have been some incidents of Islamist violence, increasingly carried out by members of powerful tribes that are traditionally the backbone of support for the ruling Hashemite dynasty.

Security forces have been extra vigilant having warned that sympathizers of Islamic State could launch revenge attacks after militants were driven out of most of the territory they once controlled in Syria and Iraq.

Intelligence officials and some experts believe widening social disparities and a perception of official corruption are fuelling a rise in radicalization among disaffected youths in a country with high unemployment and growing poverty.