Pakistan has condemned a suicide bomb attack in Iran and denied suggestions from the Iranian president that "some security agents" in Pakistan were cooperating with the bombers.
Iranian state television said 42 people were killed in Sunday's attack on the elite Revolutionary Guards in the country's volatile southeast.
"Pakistan is not involved in terrorist activities ... we are striving to eradicate this menace," Foreign Ministry spokesman Abdul Basit told the Daily Times newspaper on Sunday. Basit was not available for comment on Monday.
Pakistan's Prime Minister Syed Yusuf Raza Gilani strongly condemned the "ghastly act of terrorism" in Iran, Gilani's office said.
Pakistan has in the past backed Sunni Muslim militant groups, particularly in Afghanistan in the 1980s, when it supported militants battling Soviet occupiers.
Pakistan also supported militants who have been battling Indian security forces in the disputed Kashmir region.
Both Afghanistan and India say Pakistan has maintained links to some militant groups. Iran's President Mahmoud Ahmadinejad was quoted as saying security agents in Pakistan were cooperating with the militants behind Sunday's bombing, the semi-official Fars News Agency reported.
"We were informed that some security agents in Pakistan are cooperating with the main elements of this terrorist incident ... We regard it as our right to demand these criminals from them," Ahmadinejad said, without giving details.
Ahmadinejad called on Pakistan not to waste time in cooperating with Iran in apprehending the perpetrators.
Relations between Iran and Pakistan have been generally good in recent years and the neighbours are cooperating on plans to build a natural gas pipeline link.
But Iran has in the past accused Pakistan of hosting members of the Sunni insurgent group Jundollah, Iranian state television said. Iranian media say Jundollah claimed responsibility for Sunday's bombing.
Some analysts believe Jundollah has evolved through shifting alliances with various parties, including the Taliban and Pakistan's ISI intelligence service, who saw the group as a tool against Iran.
State television said Iran's Foreign Ministry summoned a senior Pakistani diplomat in Tehran, saying there was evidence "the perpetrators of this attack came to Iran from Pakistan".
"The Pakistani official assured Tehran that his country would take all measures to secure its border with Iran," English-language Press TV added.