A member of the Iranian Parliament's National Security Committee, Javad Karimi Qoddousi, said on Wednesday that the blast at Iran's main nuclear establishment in Natanz on July 2 was caused by a "security breach", Radio Farda reports.
He strictly ruled out "a strike on the complex by an external object" and added, "If it was from the outside, we should have seen shrapnel, but there are absolutely no remnants left on the site."
However, he did not elaborate further on the "security breach" or "infiltration."
On July 2, Iran reported an "incident" at the Natanz complex, but said it caused no casualties and failed to stop enrichment work at the facility.
An unnamed Middle Eastern intelligence official later told The New York Timesthat Israel was responsible for the attack, which he said was carried out using a powerful bomb. Israel has not commented on the report.
Last week, Iran warned that any country found to be responsible for the explosion at Natanz should expect retaliation.
The explosion at Natanz came six days after an explosion near a military complex in Parchin area southeast of Tehran rocked the Iranian capital.
Authorities blamed that blast on "leaking gas tanks".