"In the letter, Mr Jalili complains of the attitude of the West and says their approach has harmed the constructive process of negotiations between the two parties," the official told AFP, declining to be named.
The letter was to be delivered to Solana later on Monday by Iran's ambassador in Brussels, and copies were to go to the foreign ministers of the five UN Security Council permanent members — Britain, China, France, Russia and United States — plus Germany.
Western countries hit out at Iran at a meeting in Vienna last month over its refusal to disprove allegations of past nuclear weapons work and for pursuing uranium enrichment in defiance of UN demands.
The International Atomic Energy Agency's latest report on its six-year probe into Tehran's contested nuclear drive "presents a decidedly bleak picture," German ambassador Ruediger Luedeking told the IAEA's 35-member board.
"Iran continues to defy the requests of the international community," Luedeking said, speaking on behalf of the so-called EU-3 of France, Germany and Britain.
The UN Security Council has slapped three rounds of sanctions on Iran for refusing to suspend uranium enrichment, a process which can be used to make the fissile material for a nuclear bomb.
French ambassador Francois-Xavier Deniau, speaking on behalf of the 27-country EU, was also sharply critical of Iran, "deploring" its lack of transparency.
The fact that Iran was refusing both to suspend enrichment and to clear up the allegations of weaponisation studies was "alarming," Deniau said.
Iran says it has a right to enrich uranium to make nuclear fuel as a signatory to the nuclear Non-Proliferation Treaty (NPT), and denies allegations of seeking atomic weapons.
