Prince Khaled al-Faisal al-Saud made the warning during a press conference on the annual hajj pilgrimage in Mecca.
The prince – who is also governor of Islam’s holiest city – warned that there could be an eventual military dimension to the propaganda war between Iran and Saudi Arabia.
“If they are preparing an army to invade us, we are not easily taken up by someone who would make war on us,” he said.
Saud’s remarks follow escalating tensions between the Shia-majority Iran and Sunni-majority Saudi Arabia.
Both countries broke diplomatic ties earlier this year, when a row over a crush during the 2015 hajj – which left hundreds of Iranian pilgrims dead – led to a bitter war of words.
For the first time in three-decades, Tehran banned its nationals from travelling to Saudi Arabia for this year’s hajj.
It followed failed talks on logistics for the hajj in May with Iran, which takes place in the kingdom’s western Hijaz region.
Iran’s supreme leader Ayatollah Ali Khamenei questioned Saudi Arabia’s right to manage Islam’s holiest sites and called the kingdom’s rulers “puny satans”.
Khamenei also said Saudi authorities “murdered” the stampede victims.
Saud said that the “orderly conduct” of this year’s pilgrimage was “a response to all lies and slanders made against the kingdom”.
In a message to the Iranian leadership he added “I pray to God Almighty to guide them and to deter them from their transgression and their wrong attitudes toward their fellow Muslim among the Arabs in Iraq, Syria, Yemen and around the world”.
Iran has sent thousands of fighters to help prop up the Syrian regime, and is also accused of supporting Shia militias in Iraq.
Riyadh also accuses Tehran of being a key military sponsor of the Houthi rebels in Yemen, where Saudi Arabia has launched an extensive air and group campaign against the rebels.
|If they are preparing an army to invade us, we are not easily taken up by someone who would make war on us.
– Prince Khaled al-Faisal
No Iranian leader has formally called for war with Saudi Arabia but diplomatic ties were strained in January.
The countries have been involved in a slanging match over the hajj since last week.
Saudi Arabia’s Grand Mufti Abdulaziz al-Sheikh told a newspaper that Iranians “are not Muslims”.
Over 1.8 million Muslims from around the world have been attending the annual pilgrimage which comes to a close on Thursday.