MOSCOW, March 4 (Reuters) - Russian forces killed a senior Islamist rebel in the volatile southern region of Ingushetia, Russian news agencies reported on Thursday, citing law-enforcement sources.

Alexander Tikhomirov, also known as Said Buryatsky, was killed on Tuesday in a gun battle near Nazran, Ingushetia's largest town, state-run RIA news and Interfax reported.

Tikhomirov took responsibility for the deadliest attack in Russia's North Caucasus region in four years when a suicide bomber killed at least 20 people and injured 138 at a police building in Ingushetia last August.

"Tikhomirov was among six rebels killed on Tuesday in Nazran," RIA quoted an official as saying. "His body was identified on Wednesday".

An upsurge in violence in Ingushetia, Chechnya and neighbouring Dagestan has alarmed the Kremlin nearly a decade after government forces defeated Chechen rebels in the second of two separatist wars.

The violence has undermined Moscow's control over a vulnerable border area adjacent to crucial oil and gas pipelines in the South Caucasus which flow west to Europe. It has also prompted fears of attacks elsewhere in Russia.

A spokesman for Ingushetia's leader Yunus-Bek Yevkurov said he could not confirm the report of Tikhomirov's death.

(Writing by Conor Humphries; Editing by Robin Pomeroy)

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