A militant Islamist group has claimed responsibility for two explosions in a western Kazakh oil city after threatening violence in the Central Asian state, a U.S.-based online monitoring service said.

The suspected bomber was the only person killed in the blasts Monday, which occurred close to administrative buildings in Atyrau, close to the Caspian Sea about 2,500 km (1,553 miles) west of the capital Astana.

Intelligence monitoring group SITE said a message on an online forum attributed to the Jund al-Khilafah group said the bombings were a response to the government's indifference to its warnings to repeal new laws restricting religious freedoms.

Mainly Muslim Kazakhstan adopted new legislation last month that bans prayer rooms in state buildings and requires all missionaries to register with authorities every year.

President Nursultan Nazarbayev, who has ruled Kazakhstan as a secular republic since independence from the Soviet Union, has backed the law as a means of stamping out religious extremism in a country which has been largely untouched by militant attacks.

Several unexplained bombings and shootouts this year have raised concerns about growing militancy. Authorities moved to adopt the new law soon after security forces in August detained 18 people in Atyrau on suspicion of planning acts of terror.

News agency Novosti-Kazakhstan quoted Bolat Daukenov, deputy governor of Atyrau region, as saying Monday's bombings were the last breath of the group of people arrested.

Jund al-Khilafah (Soldiers of the Caliphate) said it would carry out more attacks unless the law were repealed, SITE reported. The group denied reports it was a suicide attack and said the person carrying the bomb died when it exploded accidentally.

The previously unknown militant group last week issued a video dated October 21 warning of violence unless the government abolished the religion law.

The group also criticised the authorities for banning headscarves. In fact, there is no provision in the law that restricts religious headwear.

The Atyrau region prosecutor's office said it had identified the bomber as a local 24-year-old man, Novosti-Kazakhstan reported.

Home-made explosive devices and instructions for assembling them were found during a search of his home, the agency cited the prosecutor's office as saying.

(Writing by Robin Paxton; editing by Andrew Roche)