Iraq's disbanded Ba'ath party threatened to attack the heavily-protected "Green Zone" in Baghdad if the death sentence is carried out against its leader Saddam Hussein, in an Internet statement posted on Tuesday.
"If president Saddam Hussein is executed ... the party will reinforce its siege against the Green Zone," which houses Iraqi government offices and the US embassy, said the party's command on its official site.
It vowed to "use all possible means to destroy embassies, as well as the headquarters of intelligence and treacherous organisations".
"America and Iran, its ally, have detonated a bomb whose shrapnel will hit all the plotters and their agents in Iraq and outside," said the party statement, referring to Sunday's death sentence against the ousted president.
Saddam, 69, was sentenced to hang for committing crimes against humanity by ordering the deaths of 148 Shiites from the village of Dujail, north of Baghdad, after a 1982 assassination attempt against him.
On Tuesday the former strongman was back in court to hear further testimony on how he and six other Saddam regime officials allegedly massacred tens of thousands of Kurds in 1988 during the Anfal campaign in northern Iraq.
A top official in Baghdad said Monday that Iraqi leaders have agreed a draft law to allow former Baath members back into government jobs.
Ali al-Lamy, head of the Supreme National Council for De-Baathification, said the proposed reform could reverse the sacking of more than a million former Baath party activists, mainly members of Iraq's Sunni minority.