Pakistan and Iran Jockey for Influence after Bombings ISLAMABAD (Reuters) - As tension grows between Pakistan and Iran after a mosque bombing in Iran, Pakistan could find itself increasingly isolated as its western neighbour looks to increase its influence in the region, analysts say. Jundollah, a Sunni Muslim militant group Iran says is based in Pakistan's southwestern province of Baluchistan, claimed responsibility for a December 15 double suicide bombing in the Iranian town of Chabahar that killed 39 people and wounded more than 100. Iran has demanded Pakistan take action with Iranian President Mahmoud Ahmadinejad calling this week on his Pakistani counterpart, Asif Ali Zardari, to arrest "identified terrorists" and hand them over to Iran. Iran says Jundollah fighters find shelter in Pakistan. Pakistan denies providing shelter for the group. But in an echo of U.S. demands regarding Taliban sanctuaries in northwest Pakistan, a member of the Iranian parliament's national security and foreign policy committee suggested that if Pakistan didn't act, Iran would. Analysts say the strong words from Iranian officials add to growing international pressure on Pakistan to take stern action against militants operating out of its territory. In a review of Afghanistan strategy unveiled last week, the White House hailed Pakistan's steps against militant groups, but said war-torn Afghanistan could not be stabilised unless Pakistan acted decisively against militants sheltering there. Analysts say Iran may also may be seeking to exploit Pakistan's vulnerability in the face of pressure over its inability or unwillingness to fight militants operating from its soil, to increase its influence as a regional power. "Iran is ... a major regional stakeholder in Afghanistan and a competitor of Pakistan there. It is therefore likely that Iran is now flexing its muscles on its eastern flank to showcase its regional rise," the intelligence firm STRATFOR said. Pakistan and Iran have long jockeyed for influence in Afghanistan, with Pakistan supporting the ethnic Pashtun and Sunni Muslim Taliban and pre-dominantly Shi'ite Iran backing the Taliban's enemies in the old Northern Alliance of non-Pashtuns and some Shi'ite groups. PLACATING IRAN STRATFOR said Pakistan would try to address Iranian concerns as it already had had tense relations with its two neighbours -- India and Afghanistan -- over militant violence. Both accuse Pakistan of supporting or tolerating militants targeting them. Indeed, Pakistani Interior Minister Rehman Malik said his government had assured Iran it would help track down perpetrators of the mosque bombing. "We have assured them that we will arrest and hand over any Iranian terrorist found in Pakistan and we have asked them to give us specific information," Malik told Reuters. A Pakistani official said in February Pakistan had helped Iran arrest of Jundollah leader Abdolmalek Rigi, amid contradictory reports about how he was detained. But any trust built by the arrest was dashed by subsequent bombings. Relations between Pakistan and Iran have been marked by wariness since the 1979 Iranian Revolution brought a radical Shi'ite strain to power in Tehran. But both sides have generally publicly refrained from accusing each other of fomenting trouble. That's changed, though, with the recent attacks in Iran claimed by Jundollah. Iran, locked in a showdown with the United States over its nuclear programme, links Jundollah to the Sunni Islamist al Qaeda network and says it enjoys U.S. backing. The United States denies that. Security analyst and author Ahmed Rashid said Jundollah had evolved through shifting alliances with various parties, including the Americans, the Taliban and Pakistan's intelligence services, who all see the group as a tool against Iran. Iran is sceptical of Pakistan's denial it is helping the group. "There is mistrust for Pakistan all over. It's from neighbours, from allies, from everywhere," Rashid said. "It's a very dangerous situation."