Mission chief Adam Kobieracki attempted to appease concerns about the role of the observers from the Organisation for Security and Cooperation in Europe, who are fanning out to 10 cities across both sides of the crisis-hit nation.
The pan-European security watchdog deployed the mission after Russia's annexation of Crimea -- following a change of government in Kiev -- sent tensions soaring between pro-Moscow separatists and Ukrainian nationalists.
The mission is made up of 100 civilian monitors deployed for six months, but may rise to up to 500 members.
"We are not spies, we are friends," Kobieracki insisted.
Violent protests have hit Kharkiv and another eastern city, Donetsk, as some citizens demand to follow in Crimea's footsteps and join former Soviet master Russia.
Local journalists asked Kobieracki about alleged attacks on pro-Russian demonstrators by nationalist militants from the Right Sector, a movement that played a prominent role in protests that ousted president Viktor Yanukovych in February.
A small group of protesters rushed to the front of the room, one of them interrupting proceedings to read a statement to Kobieracki.
