TEHRAN (AFP/Reuters) - A suicide bomber blew himself up on Sunday at a meeting in southeastern Iran of the elite Revolutionary Guards, killing seven commanders and 42 other people in an attack Tehran blamed on Washington. Irans armed forces accused the US and Britain of involvement in the attack and warned of revenge, the semi-official Fars News Agency reported. The Revolutionary Guards will deliver a crushing response to those behind the suicide attack, a top Guards officer said. The Guards will give a very harsh and crushing response to this group, so the group will never be able to launch another act like this in the country, General Mohammad Pakpour, commander of Guards ground forces, was quoted as saying by Fars news agency. The headquarters of the armed forces blamed the bombing on terrorists backed by the Great Satan America and its ally Britain. Not in the distant future we (Iran) will take revenge ... and Baluchis will clear this region from terrorists and criminals, Fars quoted a statement as saying, referring to the inhabitants of Sistan-Baluchestan province, where the attack took place. Several tribal leaders at the meeting in Sistan-Baluchestan province - a hotbed of Sunni insurgency - also died in the blast which officials said additionally injured 28 people. The attacker set off his explosives belt as a meeting of Guards commanders and tribal chiefs got underway around 8.00 am (0430 GMT) at a gymnasium in the city of Pisheen, near the border with Pakistan, the state broadcaster said. The number of martyrs from the terrorist attack has reached 49... and that figure could still rise, the Mehr news agency reported. Provincial chief coroner Abbas Amian told the official IRNA news agency that his office had received 42 bodies. Irans parliament speaker said the US was behind the attack while the Guards accused Western powers for the assault. The chief prosecutor in Sistan-Baluchestan said Abdolmalek Rigi, the head of the shadowy group, Jundallah (Soldiers of Allah) which is linked by some analysts to the Taliban in Pakistan had accepted the responsibility for the attack. Based on the latest information... between 30 to 35 people, including military officers, tribal leaders and local citizens, have been martyred in the attack, the chief prosecutor, Mohammad Marziah, said, as quoted by ISNA news agency. So far no one has been arrested, but terrorist Malek Rigi has accepted the responsibility for this terrorist attack, he said. Fars news agency said the bomber struck when Guard officers were meeting local leaders of the Shias and Sunnis, adding some tribal chiefs were among the dead. Fars said among the dead were Gen Nur-Ali Shushtari, deputy commander of the Revolutionary Guards ground forces, Gen Mohammad-Zadeh, commander of the Revolutionary Guards in Sistan-Baluchestan province, the Guards commander for the town of Iranshahr and the commander of the Amir al-Momenin unit. Three other commanders from the adjacent province of Kerman were also killed, according to Fars. President Mahmoud Ahmadinejad ordered Iranian authorities to swiftly track down and punish those behind the attack. Ahmadinejad said the criminals who committed ... crimes against humanity ... will be seriously dealt with, the official IRNA news agency reported. I am ordering the relevant officials to identify quickly the elements of this terrorist crime and hand them over to the judiciary, Ahmadinejad was quoted as saying by IRNA. I assure the Iranian people, especially the dear people of Sistan-Baluchestan that the criminals will receive very soon a response to their inhuman acts. Parliamentary speaker Ali Larijani said the US was implicated in the deadly attack. Mr Obama has said he will extend his hand towards Iran, but with this terrorist action he has burned his hand, Larijani said referring to US President Barack Obamas repeated diplomatic overtures to Tehran. The United States condemned the suicide bombing and denied any involvement in the attack. We condemn this act of terrorism and mourn the loss of innocent lives, State Department Spokesman Ian Kelly said in a statement in Washington. Reports of alleged US involvement are completely false, he added. Monitoring Desk adds: Following the suicide attack on Revolutionary Guards, Iran has closed its border along Pakistan.