TEHRAN (Reuters/AFP) - Iran could do away with the post of a directly elected president, Supreme Leader Ayatollah Ali Khamenei said on Sunday, in what might be a warning to Mahmoud Ahmadinejad and possible successors not to overstep the executives limited powers. Khameneis comment came with Ahmadinejad battling constant criticism from hardline conservatives accusing him of being in the thrall of deviant advisers who want to undermine the role of the Islamic clergy, including the office of supreme leader. Khamenei dropped the suggestion - of what would be the biggest change in Irans constitution for two decades - into a wide-ranging speech, saying there was no problem in eliminating the directly elected presidency if deemed desirable. Presently, the countrys ruling political system is a presidential one in which the president is directly elected by the people, making this a good and effective method, he told an audience of academics in the western province of Kermanshah. However, if one day, probably in the distant future, it is deemed that the parliamentary system is more appropriate for the election of officials (holding) executive power, there would be no problem in altering the current structure, Khamenei said in the speech broadcast by state television. Khamenei also warned Tehran would respond robustly to any inappropriate measure by Western powers linked to an alleged Iranian plot to kill the Saudi ambassador to Washington, state television reported. Any inappropriate measure against Iran, whether political or security-related, will be strongly confronted by the Iranian nation, Khamenei said. Khamenei said Washington had fabricated the allegation to overshadow protests in the United States against corporate greed. Meanwhile, President Mahmoud Ahmadinejad on Sunday denied US allegations that Iran was involved in a plot to kill the Saudi envoy to Washington, insisting that assassination belongs to you Americans. The cultured people of Iran do not need to resort to assassination, the state television website quoted Ahmadinejad as telling a gathering of schoolchildren in Tehran. His comments reinforced fierce denials made by other Iranian officials since Washington first made the allegations on Tuesday. The Iranian government has also repeatedly accused the United States and Israel of being behind the assassinations of two of its nuclear scientists in the past two years. Ahmadinejad said: They (the United States) are trying hard to push the anti-Iran campaign and in this phase they have accused Iran of assassination, but we must make them understand that assassination is the work of an uncultured people. One day they impose a war, the next they impose economic sanctions and the next, political pressure, he added. Meanwhile, Saudi Arabia has taken a first step to have Iran reported to the United Nations Security Council, a move that could lead to new sanctions. Saudi Arabias permanent mission to the United Nations... formally requested the United Nations Secretary General notify the Security Council of the heinous conspiracy, the Asharq al-Awsat newspaper reported, citing a statement from the kingdoms UN mission. The Saudi step follows remarks by US President Barack Obama that he would press for the toughest possible sanctions against Iran over the alleged plot, and vowed not to take any options off the table - a phrase commonly used to mean the possibility of using force. Saudi Foreign Minister Prince Saud al-Faisal said on Wednesday in Vienna that Iran was responsible for the alleged plot and said Riyadh would adopt a measured response.