More than 140 people have been killed in blasts targeting Iraqi Shias celebrating a holy day in Karbala and Baghdad.
World leaders and members of the Shia community have expressed shock and outrage - and some focused blame.
The (UN) Secretary-General (Kofi Annan) condemns in the strongest possible terms
today's terrorist attacks in Karbala and Baghdad. He is particularly
appalled that these incidents took place in and around Muslim
shrines during the holy occasion of Ashura.
Mr Annan "urges all Iraqis to refrain from acts that could
undermine efforts to achieve national reconciliation at this
delicate stage of the country's political situation.
Kofi Annan's spokesman
We condemn these brutal terrorist attacks in the strongest
There are enemies of freedom in Iraq, who seek to undermine a
peaceful and democratic future for the Iraqi people. They will fail.
Democracy is taking root and it cannot be turned back.
Spokesman for the White House
These are barbarous acts that we condemn in the strongest
German Foreign Minister
[The attacks were designed to] try and set the different
religious communities in Iraq against each other... when the vast majority of people in Iraq want to build an Iraq that is stable and free and prosperous and democratic for the future.
British Prime Minister
This blatant crime against innocent people leaves one amazed and astounded as to how anyone can - in a spiritual atmosphere and at holy sites - commit this terrorist deed, massacring innocent and defenceless people who are mourning because of their love for their sanctities.
Without a doubt the people who have committed these crimes know nothing about humanity and, unfortunately, the continued presence of occupying forces has been unable to provide security for the Iraqi people, and they must accept their responsibility in this respect.
Hamid Reza Asefi
Spokesman for Iranian Foreign Ministry
It is natural that the whole finger of accusation will be pointed at the occupiers, because the responsibility for security in Iraq currently lies with the occupiers, who have been occupying Iraq for nearly a year.
Hence, we have to say that Iraqis are in the right in the current circumstances when they consider the Americans responsible for these killings and this shedding of blood.
Iranian state radio commentary
How is it possible that any man - let alone a Muslim man -
does this on the day of al-Hussein? Today war has been
launched on Islam.
Shia al-Dawa party in Iraq
This criminal act, on the holy day that marks the martyrdom
of Hussein, shows that the terrorists respect no boundaries,
that they will kill visitors, pilgrims from Iraq and innocents
of all kinds.
Council for the Islamic Revolution in Iraq
I came here [Karbala], I saw the explosions and I saw the victims.
The criminals are trying to strike discord in Iraq, but we are
going to fight them until the very last drop of our blood.
Mohammed Bahrul al-Ulum
Current president of the Iraqi Governing Council
The main aim is to create problems between the Sunni and Shia
We have to be very careful.
Kurdish member of the Iraqi Governing Council
This is a message from [Abu Musab] al-Zarqawi [an extremist believed to be linked to
al-Qaeda] to the Iraqi people and we received the message.
It is written in blood now. We will not respond in a sectarian way.
Shia member of the Iraqi Governing
These cowardly attacks by desperate terrorists will not succeed
in stopping the people of Iraq along the road to democracy, notably
after the signing of the temporary constitution.
The Iraqi people will overcome this test.
Spokesman for the Iraqi National Congress (INC)