Javier Solana arrived in Saudi Arabia on Monday and told reporters: "Be sure we are going to do our utmost for this not to happen again, because we need each other ... I don't think honestly it will happen again."
Solana did not elaborate. He was speaking after talks in Jedda with the head of the Organisation of the Islamic Conference, representing 57 Muslim countries.
Solana has said he hopes to begin quelling the furore over the cartoons during his visit.
He was due to meet King Abdullah in the capital, Riyadh, before heading to Egypt, Jordan, the Palestinian territories and Israel.
Protesters have attacked the Danish and Norwegian missions in Damascus, Beirut and Tehran over the cartoons, which first appeared in a Danish newspaper last September. They have been republished in many papers around the world.
Muslims consider any portrayal of the Prophet blasphemous.
Saudi Arabia recalled its ambassador from Denmark last month after pressure from clerics and a popular campaign against Danish products in the kingdom, the site of Islam's holiest shrines.