The new US ambassador to Baghdad says the next few months are critical to reconciling Iraq's warring communities.
The wall is being constructed at night under heavy security
In his first news conference, Ryan Crocker urged the government to make use of a US security plan in Baghdad.
"I think the Baghdad security plan can buy time for what it ultimately has to be, a set of political understandings among Iraqis," Mr Crocker said.
He also defended the thinking behind a controversial wall being built around the flashpoint Adhamiya neighbourhood.
On Sunday Iraqi Prime Minister Nouri Maliki said he had ordered a halt to the building around the Sunni enclave on the mainly Shia east bank of the Tigris, after the project drew strong criticism from residents and Sunni leaders.
Violence has continued with three suicide bombers killing at least 27 people and wounding nearly 60 in various parts of Iraq, including one close to where Mr Crocker was speaking.
Mr Crocker said the US would "obviously... respect the wishes of the government and the prime minister" regarding the Adhamiya wall.
But later in the press conference he added that building the barrier made "sound security sense".
Correspondents say Adhamiya suffers incursions from neighbouring Shia areas and often comes under mortar attack.
However, the wall would help security forces to control the movement of militant Sunni groups for whom Adhamiya is a stronghold.
"It is in no-one's intention or thinking that this is going to be a permanent state of affairs," said Mr Crocker.
Construction of the 5km (3-mile) concrete structure began on 10 April and the US military had said it hoped to complete the project by the end of the month.
One of Monday's attacks hit a restaurant just outside the Green Zone where Mr Crocker was speaking, killing at least six people and leaving 16 wounded.
Another car bomb exploded close to the Iranian embassy in Baghdad. One person was reported killed in the blast, in a car park used by people visiting the Iranian mission.
There were also suicide car bombings outside a Kurdish party office in the town of Tal Uskuf near Mosul and outside a Baqouba police station.
Ten people were reported killed in each attack and more than 20 wounded.
An eyewitness in the mainly Christian town of Tal Uskuf said residents were in deep shock as it was the first time it had been hit in the four years of Iraq's anti-US insurgency.