"It is a matter of urgency to provide a prompt and consolidated international response to this act of aggression. Declarations are not enough. There must be action," Pavlo Klimkin told the annual gathering of OSCE ministers.
"We must raise the cost for Russia with comprehensive and tailored sanctions ... There can be no business as usual."
The 57-nation OSCE, a security and human rights watchdog, has been rattled by the military and diplomatic stand-off between Russia and Ukraine, both of whom are member states.
While numerous Western ministers voiced robust support for Kiev, Russian Foreign Minister Sergei Lavrov pinned the blame for years of escalating tensions on Ukraine and its allies.
"Striving for dominance, a small group of countries uses blackmail, pressure and threats," Lavrov told the gathering in a cavernous conference center in Italy's financial capital.
"Kiev (is) free from any punishment, shielded by its Western sponsors, who justify all its outrageous actions," he said.
The United States and the European Union have imposed sanctions on Russia since 2014, when Moscow annexed Crimea, previously Ukrainian territory, after a pro-Russian leader was toppled in Kiev.
Fighting between Ukraine and Moscow-backed separatists in the Donbass region of eastern Ukraine has killed more than 10,000 people. Major fighting ended with a 2015 ceasefire but deadly exchanges of fire are still frequent.
The unresolved crisis returned to the fore last month when Russian patrol boats fired on and seized three Ukrainian vessels in the Black Sea and captured 23 sailors.
Moscow has accused Kiev of orchestrating the clash, saying the Ukrainian boats had entered Russian waters -- something Ukraine denies. Lavrov said on Thursday the move was a "provocation" and charged that Ukraine was seeking to sabotage any efforts to restore peace in the region.
But U.S., Canadian and European ministers lined up on Thursday to denounce Moscow and pledge their support to Kiev.
"Russia's illegal annexation of Crimea, its direct involvement in the conflict in the Donbass and now its illegal actions targeting Ukrainian sailors and vessels ... cannot and must not be accepted by the international community," said Canada's foreign minister, Chrystia Freeland.