Russia would violate international agreements if it placed nuclear weapons in Crimea, which it annexed from Ukraine, Ukraine's Prime Minister Arseniy Yatsenyuk said Tuesday.
Russian Foreign Minister Sergei Lavrov appeared to reserve the right for Russia to put nuclear weapons in Crimea in comments to Russia's Interfax news agency on Monday.
Lavrov said while Crimea had been part of nuclear weapons-free Ukraine, that was no longer the case and the peninsula was no longer a non-nuclear zone under international law.
"Crimea became part of a country that possesses such arms. … The Russian state, in line with international law, has the right to manage its nuclear arsenal … in accordance with its interests and international legal obligations," he said.
Yatsenyuk, visiting Brussels for talks with European Union and NATO officials, said Crimea was Ukrainian territory and nuclear weapons could not be deployed in Ukraine.
Lavrov's comments were "another sign that this is not just a conflict between Ukraine and Russia," he said, accusing Moscow of breaking the nuclear non-proliferation treaty.
Under the 1994 Budapest memorandum, Russia, the United States and Britain gave Ukraine security assurances in return for Kiev giving up its Soviet-era nuclear weapons and signing the nuclear non-proliferation treaty.
"Russia is constantly violating international law. Russia is constantly intimidating NATO member states, for example through the violation of [their] air space with Russian jets, and Russia started to violate nuclear non-proliferation treaties," Yatsenyuk said at a European Policy Centre think tank event.
"This is the challenge for the entire world," he said.
Yatsenyuk also said Russia was paying the price for its intervention in Ukraine, pointing to the plunging ruble, high inflation, limited access to international financial markets, and the sliding oil price.
The ruble plunged more than 11 percent against the dollar on Tuesday in its steepest intraday fall since the Russian financial crisis in 1998 as confidence in the central bank evaporated after an ineffectual rate hike.
Russian President Vladimir Putin had underestimated EU and U.S. unity over sanctions, Yatsenyuk said.
Asked about prospects for tighter sanctions on Russian energy, Yatsenyuk said: "They are already in place … 40 bucks [dollars] per barrel sounds not bad."
Oil fell below $59 a barrel for the first time since May 2009 on Tuesday. Concern over over-supply and weakening demand are seen as the main factors, not Western sanctions.