Apparently Ali Akbar Salehi, Iran's Foreign Minister, admitted to an Iranian source that they were definitely involved in the plot to kill ambassador Adel A. Al-Jubeir in Washington DC. The source allegedly told Al-Arabiya that the Revolutionary Guard was indeed involved.
According to the source, which is close to Gholam Hussein Elham, former spokesman of the Iranian government and dissident from Ahmadinejad’s regime, Salehi recently met with Mohammed Nahavandian, former assistant at the National Security Council and the current president of the Chamber of Commerce and Industry.The seven page "rant" demanded a public apology ... " to the Iranian government and its citizens for the false accusations they publicised against Tehran in violation of international norms and regulations."
In the meeting, both discussed several political and economic issues in addition to the plot to assassinate the Saudi ambassador. It was then that Salehi admitted to the Revolutionary Guard’s involvement in it.
In violation of international norms and regulations? What a joke coming from a country with some of the worst human rights violations in the world.
Of course it was an unnamed source (anonymous with good reason), so they're still mere allegations, but I was and still am convinced they were involved. It makes their demands for an apology even more laughable.