An army spokesman said the first bomb killed three and wounded one when it exploded at 19:45 GMT on Saturday in southeast Baghdad.
The fourth death followed a roadside bombing at 03:30 on Sunday morning.
The attacks bring the number of US soldiers killed in action in Iraq since its invasion and occupation to 389.
They follow the killings early on Sunday of two US occupation soldiers in an explosion in the city of Tikrit, 180km north of Baghdad. Another five soldiers were injured in the attack, some of them critically.
The fatalities may increase pressure on the US to finalise plans for a caretaker government to run Iraq from July.
Three month deadline?
US-appointed Iraqi politicians and the US-led occupation administration have three months to agree on the make-up of a new body to lead the country.
The interim government will stand until direct elections by the end of January 2005.
A spokesman for the Iraqi governing council, Hamid al-Kifai, said there was increasing pressure "to explain how the caretaker government will be formed."
He underlined that despite involving the international community, the question of how Iraq would function once it regains sovereignty from the occupying forces remained "an Iraqi affair."
A trader's ties to Iraq's Governing
Council led to his targeting
White House envoy
But Senior White House official Robert Blackwill has arrived in Baghdad to settle political rifts within the 25-member council, which signed a temporary constitution last Monday, but continues to debate the content.
Occupation spokesman Dan Senor said Blackwill would be urging the Governing Council to invite the UN back to the country to help move the political process forward.
Council members have said their immediate priorities are to fix a caretaker government and devise a system for direct elections before overcoming problems with the content of the basic law.
The text has drawn heavy criticism from the spiritual leaders of Iraq's Shia community as well as disenchanted members of the public.
Under the interim law, which cannot be altered without a 75% parliamentary majority, voters in any three of Iraq's 18 provinces can reject the permanent constitution when it is drawn up – a policy that effectively gives Kurds a veto over decisions.