TEHRAN (Reuters) - Iran, facing mounting U.S. pressure over its nuclear program, promised Thursday a "burning hell" for any aggressor as tens of thousands marched to mark the 26th anniversary of its Islamic revolution. "The Iranian nation does not seek war, does not seek violence and dispute. But the world must know that this nation will not tolerate any invasion," President Mohammad Khatami (news - web sites) said in a fiery speech to the crowd in central Tehran. "The whole Iranian nation is united against any threat or attack. If the invaders reach Iran, the country will turn into a...