World leaders deplored the catastrophe in Baghdad (search) where hundreds of people were trampled to death on a bridge or drowned in the Tigris (search) river.

Statesmen and leaders of international organizations sent their deepest condolences to the thousands of Iraqis mourning their loved ones who were killed Wednesday when a Shiite Muslim procession was panicked into a stampede.

Countries as politically far apart on Iraq as the United States and Iran — a largely Shiite country — offered to care for the injured.

"The United States deeply regrets the tragic loss of life of worshippers in Kazimiyah (search), Baghdad today," said State Department spokesman Sean McCormack in Washington. "Our sincere condolences and thoughts and prayers go out to the many Iraqi families who lost loved ones in this tragedy.

"We pledge every effort by the United States and the multinational force in Iraq to aid the victims," McCormack added.

Iranian President Mahmoud Ahmadinejad (search) called both the Iraqi president and prime minister to express his deep regrets for the "terrorist attacks," the official Islamic Republic News Agency reported.

Ahmadinejad "proposed the establishment of a regional trio, comprised of Iran, Syria and Iraq, to seek ways to confront the problem" of terrorism, the agency reported.

The European Union (search), NATO (search) and Iran blamed the stampede on terrorists.

British Foreign Secretary Jack Straw (search), speaking on behalf of the 25-nation EU, said the stampede was "a most shocking and terrible tragedy, initiated by terrorism, and its scale almost defies imagination."

NATO Secretary-General Jaap de Hoop Scheffer (search) said: "Hundreds of innocent people, mostly women and children, have died because of the fear and panic that terrorists are sowing in Iraq."

However, some people celebrated the Shiite deaths in notes posted on militant Islamic Web sites.