An Irish Anti-War Movement protest parade on Saturday was prevented by gardaí from moving up Grafton Street, which was crowded with Christmas shoppers.
When it became apparent gardaí were not going to allow access, Mr Boyd Barrett called on the crowd to continue towards the US embassy, but not before cries of "Shame!" filled the air.
"It's very ironic they barricaded Grafton Street off to 'ensure public access'", Mr Barrett said. "We're very disappointed with their policy," he added.
Gardaí said the decision not to allow the marchers up Grafton Street on Saturday arose out of concern for Christmas shoppers and public safety.
The protestors continued their protest to the US embassy in Ballsbridge, arriving at its heavily guarded gates at 3.45 pm.
Rain-soaked leaflets were hung off the railings surrounding the embassy and white balloons were pushed through the gates.
The several hundred who took part in the march to voice their opposition to war in Iraq included trade union officials, students, and Irsh, American and Palestinian peace campaigners.
Before setting off, one of the organisers, Ms Mary Van Lieshout, urged protesters to remain peaceful.
Mr Barrett called on the gardaí "to relent" on their decision and allow the protestors their "democratic right" to go up Grafton Street, claiming gardaí were "inciting problems" by their refusal.
By the time protesters reached the bottom of Grafton Street, a double row of steel barricades had been erected, preventing shoppers and protestors alike from entering the street.
SIPTU president Mr Des Geraghty reminded the crowd of when he used to protest outside the embassy during the Vietnam War and said opposition today was as important as it was then.
"It's always the poorest, the unemployed, the downtrodden who suffer in war, not the George Bushes of this world," said Mr Geraghty. "Are we going to allow the US to recreate divisions of the past in new more technological ways?" he asked.