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By Fredrik Dahl and Reza Derakhshi
TEHRAN (Reuters) - Iran has made some arrests in connection with this week's suicide bombing that killed dozens of people but expects neighbouring Pakistan to catch and hand over the main suspects, its police chief said on Wednesday.
Pakistan said it would help Iran hunt down the culprits. Iran, a mainly Shi'ite Muslim state, says the Sunni rebel group which claimed responsibility for Sunday's attack in its volatile southeast operates out of Pakistan.
"The terrorists are based in Pakistan and the Pakistan government is responsible in this matter," police chief Esmail Ahmadi-Moghaddam said, according to Fars News Agency. "We expect that at least the heads of these groups will be handed over to our country."
He said "some elements linked to the terrorists have been arrested" by Iranian security forces, IRNA news agency reported, without giving details.
Iran's Revolutionary Guards, which lost high-ranking officers in the blast, says the militants are backed by intelligence organisations of the United States, Britain and Pakistan. Washington, London and Islamabad deny involvement.
"Without the support of the intelligence services of other countries the terrorists would not have been able to carry out that attack," said Mojtaba Samareh-Hashemi, a senior adviser to President Mahmoud Ahmadinejad, IRNA reported.
Raising the stakes, a senior Guards commander said on Tuesday his force should be given permission to confront the Sunni insurgent group Jundollah (God's soldiers) inside Pakistan, state television reported. It did not specify whether General Mohammad Pakpour was referring to authorisation for such an operation from Pakistan or from Iranian authorities.
Pakistani Foreign Minister Shah Mehmood Qureshi declined to comment on the report and said an Iranian delegation was due in Pakistan for talks. Samareh-Hashemi said Iran would present documents showing foreign intelligence involvement.
"We will help them and support them in unearthing the people responsible," Qureshi told Reuters on Wednesday. "We will sort this thing out on a government-to-government basis."
He said terrorism was a regional problem also affecting Pakistan, and the two countries had to help each other.
"IRAN WOULD ACT"
Iranian parliament member Ali Aqazadeh said: "Iran is hoping that Pakistan will take steps ... to extradite the armed rebels to Iran. Otherwise Iran would act against the rebels and their supporting government based upon international norms."
Pakistan launched a long-awaited offensive against militants in its northwest at the weekend after a string of bomb and suicide attacks rocked the country in recent weeks and killed more than 150 people.
Analysts say Jundollah, which has said Sunday's attack was a "response to the continuous crimes of the Iranian regime against the defenceless and oppressed people of Baluchestan," is increasingly inspired by Sunni militants based in Pakistan.
Iranian media say about 42 people died in the bombing that underlined deepening instability in the southeastern Sistan-Baluchestan province bordering Pakistan and Afghanistan.
Fifteen Guards members were among those killed, including the deputy head of ground forces. It was the deadliest attack in the Islamic Republic since its 1980-88 war with Iraq.
The U.N. Security Council, which heeded a request from Tehran and condemned the attack on Tuesday, put the death toll at 57. It was not immediately clear where that figure came from.
The Revolutionary Guards, seen as fiercely loyal to Supreme Leader Ayatollah Ali Khamenei, handle security in border areas. Their power and resources have increased in recent years.
Relations between Iran and Pakistan have been generally good and they are cooperating on plans to build a gas pipeline.
But Iran has in the past accused Pakistan of hosting members of Jundollah, which says it fights for Sunni rights in Iran.
Many Sunnis live in the impoverished desert area, which has seen an increase in bombings and clashes between security forces, ethnic Baluch Sunni insurgents and drug traffickers.
(Additional reporting by Hossein Jaseb in Tehran and by Augustine Anthony in Islamabad; editing by Mark Trevelyan)