* Group claims attempt to assassinate Ingush president

* Web claim says bombing ordered by wanted separatist leader

* Restive southern regions pose challenge to Kremlin

MOSCOW, June 28 (Reuters) - The Chechen rebel group behind the 2004 Beslan school massacre has claimed responsibility for a suicide bombing last week that badly wounded the president of Russia's southern region of Ingushetia. "This operation was carried out by the rebel battalion Riyadus Salikhin," the group said in a statement posted on www.kafkazcenter.com, an internet site with ties to the Chechen separatist movement.

It said the June 22 attack on Ingush president and Kremlin appointee Yunus-Bek Yekurov was ordered by Chechnya's most wanted separatist leader, Doku Umarov.

Chechnya's pro-Kremlin leadership said on June 8 that Umarov had been severely wounded in a special operation that killed four of fighters. It has been unclear since then whether he is dead or alive.

Russia has stabilised Chechnya after two separatist wars since the mid-1990s, but nearby Ingushetia and Dagestan have replaced it as the main centres of violence on the country's volatile southern flank. The restive regions pose a challenge to Kremlin rule and provide a foothold for Islamist militants.

Describing the bomb attack, the Riyadus Salikhin group said: "At 8.30 in the morning, a car packed with explosives rammed into the armoured Mercedes belonging to Yekurov."

Yevkurov, 45, underwent surgery after the bombing, which killed one of his relatives, and is now in a stable condition. Russian President Dmitry Medvedev has condemned the attack as a "terrorist act" and vowed a "direct and severe response".

Units of the Riyadus-Salikhin group, then run by Chechen warlord Shamil Basayev, who died in 2006, carried out the 2004 Beslan school siege in southern Russia in which more than 320 people died. Most of the victims were children.

(Reporting by Amie Ferris-Rotman, editing by Mark Trevelyan)

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