SURKHAKHI, Russia (Reuters) - More than 3,000 people gathered Monday in the Russian republic of Ingushetia to bury an opposition campaigner whose murder rights groups say has underlined the slide into violence across the North Caucasus.

Concern has mounted in recent months over the murders of human rights activists and reporters with links to the patchwork of republics which make up Russia's southern flank in the Caucasus mountains.

Maksharip Aushev, 43, who campaigned against what he said were abductions by the security forces, died at the wheel of his car after his vehicle was peppered with bullets as he drove to visit relatives in the nearby republic of Kabardino-Balkaria.

Mourners gathered in drizzle at a graveyard in the village of Surkhakhi, about 10 km (6 miles) outside Ingushetia's biggest city, Nazran, to bury Aushev at a family plot.

"The situation is so bad that it simply cannot get any worse after the murder of Maksharip. This is the absolute limit," said Bakha Chapanov, a 51-year-old journalist in Nazran.

Rights groups called on Russian leaders to condemn the murder and ensure those responsible were brought to justice.

"There needs to be a clear condemnation of this kind of killing by the Russian leadership because what happens at the highest level sends a signal to those below," Allison Gill, the Russia office director of Human Rights Watch, told Reuters.

"One of the problems in Russia is that there has now been a long history of people who speak out, of reporters, of human rights workers and especially activists in the North Caucasus, and when people are not held accountable or when the leadership remains silent it does help create a climate of impunity."

There has been no Kremlin reaction to the killing so far.

At least four prominent campaigners have been killed so far this year. On January 19, Stanislav Markelov, a lawyer acting for the family of a Chechen girl murdered by a Russian army colonel, was shot in central Moscow.

On July 15, Chechen activist Natalia Estemirova was murdered by unknown assailants. In August, Zarema Sadulayeva, the head of a Chechen children's charity, and her husband Alik Dzhabrailov were found shot dead in the boot of a car.

CAUCASUS KILLINGS

Aushev, who hails from a prominent Ingush family, dived into local politics in 2007 by leading a campaign against the republic's security services who he blamed for the abduction of his son and nephew.

Human rights groups say activists and reporters are routinely subject to harassment by law enforcement agencies.

"The trend in the North Caucasus is increasing violence, increasing instability and increasing danger to those who work on justice and human rights issues," said Human Rights Watch's Gill.

The kidnapping pushed Aushev, who had a flourishing building materials business, into public opposition to former Ingush leader Murat Zyazikov.

The Kremlin removed Zyazikov in October 2008 and replaced him with Yunus-Bek Yevkurov, with whom Aushev had good relations. Yevkurov was himself seriously injured in an assassination attempt in June.

Yevkurov Monday visited the Aushev family's house in Nazran to pay his condolences, a rare sign of respect for a rights campaigner by a leader in the region. He vowed to take the investigation under his personal control.

But residents said Yevkurov must put an end to the killings which have plagued the mainly Muslim republic and turned it into the Kremlin's biggest headache in the North Caucasus.

"We need to stop this outrageous shooting of people. If Yevkurov cannot fight this then he must say so and leave his post," said Akhmed, a 42-year-old resident of Ingushetia who declined to give his surname.

(Writing by Guy Faulconbridge, editing by Jon Boyle)

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