Dozens of monks and pro-government activists staged the noisy demonstration outside UN offices, accusing the international community of drumming up false allegations of war crimes in 2009 during the final months of a separatist conflict.
The activists vowed to stage more protests if UN rights official Navi Pillay criticised Sri Lanka during her week-long mission, which they say would damage the country emerging from decades of ethnic war.
"We will not hesitate to muster the protest of the entire citizenry against the UN if attempts are made to fabricate diabolical lies against Sri Lanka," the activists said in a petition.
Carrying banners that read "Let us condemn Pillay's anti-Sri Lankan visit", the activists handed the petition to a senior UN official before dispersing.
Pillay, who has previously been accused by Colombo of overstepping her mandate, arrived Sunday for her first visit after the government dropped its public hostility to her and promised access to former war zones.