"We began studying the package from the time we received it and have been making good progress. But we found more ambiguities as we moved on," Foreign Ministry spokesman Hamid-Reza Asefi was quoted as saying.

Asefi called on European negotiators to remove the ambiguities at the earliest, saying otherwise Iran would have to put off its response to the package.

"The ball is now in Europe's court. It can accelerate Iran's response to the package by removing certain ambiguities found init at the earliest," Asefi said on the sidelines of an open session of the Majlis, or parliament.

He told the law makers that "if Europe fails to clear these ambiguities, Tehran's ongoing review and response to the package will have to be postponed."

Asefi noted that the ambiguities were found in several aspects, include political and economic issues as well as the issue of use of nuclear energy for peaceful purposes.

Tehran would raise certain questions on the proposal in Tuesday's meeting between Iranian Supreme National Security Council Secretary Ali Larijani and European Union foreign policy chief Javier Solana in Brussels, according to the spokesman.

On June 6, Solana offered Iran a six-nation incentive package concerning the Iranian nuclear issue, which had been agreed by the five permanent members of the UN Security Council plus Germany.

The United States has accused Iran of secretly developing nuclear weapons under a civilian front, but Iran has said its nuclear program is for peaceful purpose.