MOSCOW — Russia’s top diplomat on Wednesday acknowledged for the first time an official relationship with pro-Russian separatists in eastern Ukraine, the same day that one of their top leaders made a surprise appearance in Moscow to whip up support for his cause.

Russian Foreign Minister Sergei Lavrov said that after Ukrainian leaders declined Moscow’s request in late May to allow Russian humanitarian aid into eastern Ukraine, Russia started to send it in anyway – via the pro-Russian separatist forces who earlier this month punched gaping holes into the border between eastern Ukraine and Russia.

“We are trying to provide humanitarian aid to those who have not left the conflict zone yet,” Lavrov told Lamberto Zannier, the secretary general of the Organization for Security and Cooperation in Europe, at a meeting in Moscow. “We applied to the Ukrainian authorities with a request in late May for permission to deliver such aid. We were refused with an official note, so we are providing aid with the support of self-defense forces, who are worried about their fathers, mothers, wives and children.”

Sending official humanitarian aid to eastern Ukraine against the wishes of the Kiev government is a highly unusual move, particularly after Russian President Vladimir Putin pledged this week to reinforce the increasingly porous border.

Russian citizens have poured into eastern Ukraine in recent weeks to join the fight against the government in Kiev, though most of them have insisted that they are volunteers and are not working for the Kremlin.

In a sign of how open the border remains, a top separatist leader in Donetsk appeared in Moscow on Wednesday, a day after Ukraine’s prosecutor general issued a warrant for his arrest on terrorism charges.

Denis Pushilin met with Russian nationalist leader Vladimir Zhirinovsky at his office and attended a pro-separatist rally in Moscow intended as a fundraiser.