Russia's deputy defense minister Anatoly Antonov denied on Sunday it was massing troops on the Ukrainian border, saying it was observing international agreements.

"The Russian defense ministry is observing all the international agreements on limiting the numbers of troops in regions bordering Ukraine," Antonov told journalists, cited by the Interfax news agency.

A Ukrainian far-right paramilitary group that played a key role in protests that ousted pro-Moscow president Viktor Yanukovych last month said Saturday it had formed a political party.

"The Pravy Sektor (Right Sector) political party was created today," member Andriy Denissenko said in a YouTube video after a meeting held behind closed doors for security reasons.

Russian Foreign Minister Sergei Lavrov and his U.S. counterpart John Kerry will discuss the Ukraine crisis on the sidelines of a nuclear summit in The Hague next week, a Russian foreign ministry official said Saturday.

"A meeting between Lavrov and Kerry is planned on the sidelines of the summit in The Hague," to be held Monday and Tuesday, Interfax news agency quoted the official as saying.

Europe has ramped up its response to Russia's annexation of Crimea with a new round of sanctions that still fall short of Washington's moves and will have little bite, experts say.

The European Union this week slapped sanctions on 12 new officials linked to Moscow's takeover of the Crimean peninsula, bringing its blacklist to 33. Among them are Russian politicians, including Deputy Prime Minister Dmitry Rogozin, along with other members of President Vladimir Putin's inner circle and Black Sea and Crimea military commanders.

Crimea held a joint funeral on Saturday for a Ukrainian soldier and a pro-Moscow militiaman killed this week -- the first casualties since Russian forces seized the Black Sea peninsula.

"These are Crimean heroes," the Moscow-ruled region's prime minister Sergei Aksyonov said at the funeral, where Orthodox priests prayed over the open coffins laid side by side.

Kiev braced for a unity rally on Sunday after elite Russian forces stormed one of Ukraine's last Crimean bases in a march that has defied both sanctions and global isolation.

Saturday's takeover involving machinegun fire into the air and stun grenades provided the most spectacular show of force since the Kremlin sent troops into the heavily Russified peninsula three weeks ago before sealing its absorption on Friday.

Germany's foreign minister on Saturday denounced Russia's "attempt to splinter Europe" by staging a disputed independence referendum in Crimea that led to the Ukrainian peninsula's absorption by Russia.

"The referendum in Crimea... is a violation of international law and an attempt to splinter Europe," Frank-Walter Steinmeier told reporters in Kiev after meeting Ukraine's interim president Oleksandr Turchynov.

Russia on Saturday expressed hopes for the success of the OSCE monitoring mission in Ukraine, while stressing the observers were excluded from Crimea after its takeover by Moscow.

"The Russian side hopes that objective and unbiased work by international observers will help overcome the crisis inside Ukraine," the Russian foreign ministry said in a statement.

Russian president Vladimir Putin has "lost Ukraine for good" with his move to annex Crimea, former prime minister Yulia Tymoshenko said Friday in her first live television appearance since returning to the country.

Tymoshenko, who spent three years in jail on what she said were politically motivated charges before being freed last month, appealed to fellow Ukrainians to be ready to fight in the event of a Russian invasion.

In response to soaring tensions with Moscow, the Pentagon is reviewing whether a reliance on Russian rocket engines for U.S. military satellite launches poses a potential national security risk, officials said Friday.

Since 1995, the U.S. military has used the Russian-made engines on Atlas V rockets, which are often employed to send Air Force and other satellites into space.