Solana made the remark during a debate at a Brussels forum on trans-Atlantic relations. He said it remains unclear "how far the U.S. is willing to engage" with Iran.
Solana had meetings with Ali Larijani, Iran's top nuclear negotiator, in Ankara on April 25 and April 26.
More talks between EU officials and Iran have been planned for May.
The United States had not had formal diplomatic relations with Iran since the 1979-1981 hostage crisis when 52 Americans were seized by Iranian students from the U.S. embassy in Tehran and held hostage for 444 days.
Responding to Solana's comments, White House National Security Spokesman Gordon Johndroe said Washington is ready to hold talks with Iran for the first time in 27 years.
But Johndroe said the administration of U.S. President George W. Bush insists that Iran must first suspend its uranium-enrichment and reprocessing activity.
Iran has rejected demands from the United States, the European Union, and the United Nations Security Council to halt uranium-enrichment work.
Tehran says it has the legal right to carry out uranium enrichment for nuclear power generation under the Nuclear Nonproliferation Treaty. Iran denies it is involved in any effort to build nuclear weapons.
(compiled from agency reports)