Tony Blair believes the manner in which Saddam Hussein's execution was conducted was "completely wrong", his official spokesman has said.
Saddam Hussein was hanged after a lengthy trial
Mobile phone footage showed Saddam Hussein was taunted before the hanging.
Setting out comments Mr Blair is expected to make this week, the spokesman said the execution "shouldn't have happened in that way".
Earlier Chancellor Gordon Brown told BBC One's Sunday AM the events were "deplorable" and "unacceptable".
Mr Blair has been criticised for not commenting in person since the footage of the 30 December execution emerged, but he is expected to do so in the coming week.
His spokesman also said Saddam Hussein's crimes and the deaths of Iraqis at his hands should not be forgotten.
Deputy Prime Minister John Prescott, standing in for Mr Blair when the prime minister was on holiday, condemned the scenes as deplorable.
Downing Street has previously said Mr Blair supported an Iraqi investigation into the hanging.
On Wednesday the Iraqi government began an inquiry into the unofficial footage, which appeared on the internet hours after the execution.
Initial Iraqi government film showed Saddam Hussein being executed in a relatively dignified manner, but the mobile phone footage which later emerged showed the former Iraqi leader - a Sunni - being taunted with Shia slogans.
Iraqi Prime Minister Nouri Maliki has said his government could review relations with any country which criticised the execution.
He said the hanging was a "domestic affair" for the benefit of Iraq's unity.
The chancellor told the BBC the manner of the former Iraqi leader's hanging was "completely unacceptable".
Gordon Brown and John Prescott have both condemned the hanging
Mr Brown said: "Now that we know the full picture of what happened, we can sum this up as a deplorable set of events.
"It is something, of course, which the Iraqi government has now expressed its anxiety and shame at.
"It has done nothing to lessen tensions between the Shia and Sunni communities."
He added: "Even those people unlike me who are in favour of capital punishment found this completely unacceptable and I am pleased that there is now an inquiry into this and I hope lessons in this area will be learnt, as we learn other lessons about Iraq."
Following Mr Brown's remarks, Liberal Democrat leader Sir Menzies Campbell criticised Mr Blair for not yet commenting, saying: "The prime minister's continuing silence is deafening.
"His unwillingness to condemn the shameful scenes surrounding Saddam Hussein's execution does him no credit."
On Sunday, Health Secretary Patricia Hewitt, Industry Minister Margaret Hodge and shadow environment secretary Peter Ainsworth also criticised the manner of Saddam Hussein's execution.