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TEHRAN, Oct 19 (Reuters) - Iranian state television said 42 people were killed in Sunday's suicide bombing attack on the elite Revolutionary Guards in the country's volatile southeast, raising the death toll from an earlier estimate of 35.

English-language Press TV also said that dozens of people were wounded in the incident and that the Guards had vowed a "crushing" response to those behind the bombing attack.

It said senior Guards commanders, civilians and tribal leaders were among the victims, in what was one of the deadliest such attacks in the Islamic Republic in recent years.

The attack in Sistan-Baluchestan province highlighted deepening instability in a southeastern region of mainly Shi'ite Muslim Iran bordering Pakistan and Afghanistan.

Many minority Sunnis live in the impoverished area, which has seen an upsurge in bombings and other violence.

On Sunday, state media said a local rebel Sunni group called Jundollah (God's soldiers) claimed responsibility for the attack, which also wounded many people ahead of a meeting with tribal chiefs in Sistan-Baluchestan province.

The southeastern province is the scene of frequent clashes between security forces, ethnic Baluch Sunni insurgents and heavily-armed drug traffickers.

Jundollah, which accuses Iran's Shi'ite-led government of discrimination against Sunnis in the remote desert region, has been blamed for many deadly incidents over the last few years.

Iranian officials also accused the United States and Britain of involvement, a charge rejected by Washington.

The bombing and allegations of foreign involvement risk overshadowing talks between Iranian and Western officials in Vienna later on Monday intended to help resolve a standoff with the West about Iran's nuclear ambitions. (Writing by Fredrik Dahl; Editing by Charles Dick)

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