The United States on Friday condemned recent "terrorist attacks" on the soil of its arch-foe Iran, and denied claims by some officials there that it was behind a deadly bombing of a Shi'ite mosque.
The firm U.S. line followed a suicide strike on the mosque in Zahedan, restive capital of Sistan-Baluchestan province, bordering Afghanistan and Pakistan, which killed at least 25 people on Thursday.
On Friday, gunmen attacked Iranian President Mahmoud Ahmadinejad's election campaign center in the same city.
"The United States strongly condemns the recent terrorist attacks inside Iran," White House spokesman Robert Gibbs said in a statement.
"The American people send their deepest condolences to the victims and their families. No cause justifies terrorism, and the United States condemns it in any form, in any country, against any people."
Earlier, the State Department denied claims by some Iranian officials that it was involved in the attack on the mosque.
"We condemn this attack in the strongest possible terms, and extend our sympathies to the families injured and killed," State Department spokesman Ian Kelly said.
"We note with concern a recent trend of bombings of Shi'ite mosques in Iraq and Pakistan as well as in Iran and strongly condemn any kind of sectarian driven violence," he said.
"The U.S. strongly condemns all forms of terrorism. We do not sponsor any form of terrorism in Iran and we continue to work with the international community to try to prevent any attacks against innocent civilians anywhere.
"We do not sponsor any form of terrorism anywhere in the world. Never have, never will," he said when reporters said it could be inferred that United States might sponsor terrorism elsewhere.
In Tehran, Iranian officials accused the United States on Friday of "hiring" those behind a suicide bombing of the mosque, linking the attack to next month's presidential election.
"Three people involved with the terrorist incident were arrested," said Jalal Sayah, deputy governor of Sistan-Baluchestan, the province bordering Pakistan and Afghanistan where the attack took place.
"According to the information obtained they were hired by America and the agents of the arrogance," Sayah told the Fars news agency. Officials usually use the term "global arrogance" to refer to Iran arch-foe the United States.
Interior Minister Sadegh Mahsooli also pointed the finger towards the United States and Israel.