Iran has warned the United States not to attack its nuclear facilities.

At a news briefing Sunday, Iran's foreign ministry spokesman Hamid Reza Asefi warned Washington "not to play with fire" by repeatedly threatening Tehran.

The spokesman also rejected a European proposal aimed at restricting Tehran's development of nuclear fuel. 

Meanwhile, a U.S. newspaper, The Washington Post, report says the United States has been flying unmanned surveillance drones over Iran for almost a year to search for evidence of nuclear weapons programs and detect weaknesses in air defenses.

In another development, U.N. Secretary-General Kofi Annan says relying on the Nuclear Non-Proliferation Treaty is not enough to prevent what he calls a "cascade" of countries acquiring nuclear weapons.  Mr. Annan urges new  joint action, including tougher inspection rules.

Some information for this report provided by Reuters.