Islamabad/Quetta: Pakistani authorities have announced the arrest of the alleged mastermind behind two recent bombings in the main northwest city of Peshawar.

Top police official Malek Naveed Khan did not identify the suspect nor say when the arrest took place. The attacks this month killed 49 people in a market area and wounded several in a recreational facility elsewhere in the city.

Earlier, Pakistan released 11 Iranians detained near the countries' border amid tensions over a deadly suicide attack in Iran that Tehran alleges has links to Pakistani intelligence officials, police said.

Authorities had first said the 11 were members of Iran's elite Revolutionary Guards, but then reversed course and identified them only as security officers. They were arrested on Monday after shoot-out involving a car carrying smugglers, authorities said.

The arrests threatened to add to the strain between the two nations triggered by the October 18 attack on the Iranian side of the border. They came a day after the Pakistani president met Iran's interior minister and vowed to track down the perpetrators of the blast.

Police official Dadur Rehman said the paramilitary Frontier Corps released the Iranians after an investigation.

"I do not have any idea why they were released," Rehman added in a phone call with The Associated Press from the area where the Iranians were held. He said he had not been privy to the interrogation.

Pakistan has been accused of supporting militant activities in two other neighbouring countries, Afghanistan and India, greatly complicating relations with both of them. Strains in its relationship with another regional power would only add to Pakistan's problems as it battles Al Qaida and the Taliban within its borders.

One Pakistani official said three senior officers among the detainees probably belonged to Iran's powerful Revolutionary Guard.

Iran's Press TV carried what it described as a statement from the guard condemning the arrests, but saying that the 11 were not its members.