It's time for the United States to hold Iran accountable.

At a news conference in Tehran, President Hassan Rouhani, a moderate cleric who has sought to open up Iran, said his victory on Friday over a hard-line conservative challenger showed that Iranians had exercised a democratic choice.

Mr. Rouhani suggested that he remained open to dialogue with the United States. But he did not waste the opportunity to exploit the contrasting optics created by Mr. Trump’s visit with Saudi Arabia’s ruling monarchs at the moment Mr. Rouhani’s victory was confirmed.

“Mr. Trump arrived in the region at the time when he saw 45 million Iranians participating in the elections,” Mr. Rouhani said. “Then he visited a country that I doubt knows the definition of elections. The poor things have never seen a ballot box.”

He added, “I hope one day Saudi Arabia chooses this path.”

Mr. Rouhani gained further momentum from local election victories on Friday by fellow reformists and moderates in at least eight major cities, according to newly posted results. Those cities include Tehran, where supporters of Mr. Rouhani are now in position to oust its hard-line conservative mayor of 14 years.

Mr. Rouhani’s remarks amounted to an emphatic denunciation of the Saudi monarchy’s extravagant welcome for Mr. Trump in Riyadh on Saturday and Sunday and their portrayal of Iran as the destabilizing force in the region.

Rejecting American warnings about testing missiles, Mr. Rouhani said that Iran’s weapons were defensive and that the country would test them whenever it deemed necessary.

He also ridiculed the $110 billion arms deal the United States and Saudi Arabia announced during Mr. Trump’s visit, suggesting that it was Saudi Arabia’s way of making amends for the Sept. 11 attacks.

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