Zelensky is trying to build wider support for Ukraine, but Vučić has refused to apply sanctions to Russia.
Serbia is trying to join the EU and has provided aid to Ukraine and promised to help it rebuild after the war.
Earlier in the week, Zelensky said delays in receiving anti-ballistic systems from partners leads to “horrific casualties and destruction”, saying that having a stronger interceptor capability “could have saved lives” in recent deadly assaults.
The president later said the supply of interceptors from allies had been “significantly reduced” this year.
It came after Ukraine hit two oil refineries deep inside Russia along with Moscow-linked vessels in the Black Sea, which Zelensky said was intended to limit oil revenues used by Russia to “finance” its war in Ukraine.
The Ukrainian military hit Russia’s Ilsky and Syzran oil refineries during overnight attacks, causing fires at both, the Ukrainian general staff said on Saturday.
A drone also entered Bulgarian airspace on Saturday and exploded near an international gas pipeline, its prime minister said, after crossing from Romania.
Rumen Radev said it had been carrying a “significant” amount of explosives but there had been no casualties or reports of damage.
It is not yet clear where the drone came from or whether it was linked to Russia or Ukraine.
Recent mediation talks between Ukraine and Russia have faltered, leading to an escalation of attacks between both sides.
