BAGHDAD - In a second day of major bloodshed, two suicide bombers wearing explosive vests blew themselves up at the gates of a Shi'ite Muslim shrine in Baghdad on Friday, killing 60 people, Iraqi police said.

The attack was the deadliest single incident in Iraq since 63 people died in a truck bomb blast in Baghdad on June 17 last year, and came amid growing concerns that a recent drop in violence might turn out to have been just a temporary lull.

At least 125 people were wounded in the apparently coordinated blasts at the Imam Moussa al-Kadhim shrine in the Shi'ite neighborhood of Kadhimiya, police said. Many of the dead and wounded were Iranian Shi'ite pilgrims.

Police said the attackers approached two different gates to the shrine, which has been a frequent target in the past.

One of the bombers detonated the explosives just inside a courtyard of the shrine, which contains the tombs of two important holy men, or imams.

The blasts on the Muslim holy day followed two suicide bombs on Thursday, one in Baghdad and the other in the northeastern province of Diyala, in which at least 89 people died.

Most of the 57 dead in Diyala were Iranians, who have flocked to Iraq's Shi'ite holy sites in the millions since Sunni Arab dictator Saddam Hussein was ousted in the 2003 invasion.

The incident (in Iraq) yesterday was a very, very hateful example of those who harm religion in the name of religion, influential Iranian cleric and former president Ali Akbar Rafsanjani told worshippers at Friday prayers.

We feel sorry for the Iraqi people because such corrupt groups have penetrated into Iraq. We also criticize America for not having the serious will to preserve Iraq's security, Rafsanjani added.

GROWING FEARS OF RESURGENCE IN VIOLENCE

While violence in Iraq has fallen dramatically over the past year, insurgent groups such as al Qaeda still carry out frequent attacks. Suicide bombings are a hallmark of Sunni Islamist al Qaeda.

The latest attacks coincide with growing fears of a resurgence in violence as U.S. troops prepare to pull out of Iraqi cities in June, ahead of a full U.S. withdrawal by the end of 2011, and amid doubts over the effectiveness of Iraqi forces.

A national election at the end of the year has also heightened apprehensions as political parties and armed groups jostle for dominance of the oil-producing nation.

Analysts say the sectarian divide remains between Shi'ites and Sunnis, which led to tens of thousands being slaughtered, while Kurd-Arab tensions over disputed lands in the north could also provoke renewed conflict.

On Thursday, Iraqi authorities announced the arrest of a leader of an al Qaeda-linked insurgent group. But neither they nor the U.S. military were able to confirm on Friday that the person was Abu Omar al-Baghdadi, the purported head of a group called the Islamic State of Iraq (ISI).

Some experts say they remain unconvinced that Abu Omar al-Baghdadi actually exists, speculating that he is a fictional character invented by al Qaeda in Iraq (AQI).

Abu Omar al-Baghdadi is, I believe, not a real person, but a title given to an Iraqi who acts as an Iraqi figurehead of ISI/AQI so that they can claim that it is led by Iraqis when, almost certainly, it is led by foreign jihadists, said Terry Kelly, a senior researcher at the Rand Corporation think-tank.

This is not the first time there have been claims that he has been caught or killed. The previous claims may be true, said Kelly, who served as a policy adviser to the former U.S. ambassador to Iraq, Zalmay Khalilzad.

Iraq