Interim Ukrainian Prime Minister Arseniy Yatsenyuk's announcement came just days after President Vladimir Putin won parliamentary authorization to use force against Russia's neighbor in response to the sweeping of pro-Kremlin leaders from power and the installation of a new US- and EU-backed government. Russian officials did not immediately respond publicly to Yatsenyuk's comments.

"So far, [talks] have been rather timid," Yatsenyuk said in a statement issued after he and interim President Oleksandr Turchynov met US Secretary of State John Kerry during the diplomat's first visit to Ukraine since the political dissolution began in November. "But the first steps have been made."

On Tuesday, Yatsenyuk also reaffirmed his government's commitment to signing a key EU trade deal that ousted President Viktor Yanukovych had rejected in November. That decision sparked three months of protests against Yanukovych's rule that culminated in a week of carnage in which nearly 100 died, ultimately leading to the former president's exile in Russia.

'Illegal actions'

On Tuesday, Ukraine's ambassador to Austria, Ihor Prokopchuk, sent a letter to the International Atomic Energy Agency in Vienna. Addressed to IAEA Director General Yukiya Amano, the letter read: "Illegal actions of the Russian armed forces on Ukrainian territory and the threat of use of force amount to a grave threat to security of Ukraine with its potential consequences for its nuclear power infrastructure."

Ukraine has 15 nuclear power reactors in operation, accounting for nearly 44 percent of its electricity production in 2013, according to the IAEA's website. On Sunday, Ukraine's parliament called for international monitors to help protect its nuclear power plants, as tension mounted with Russia.

"Under these circumstances, the competent authorities of Ukraine make every effort to ensure physical security, including reinforced physical protection of 15 power units in operation at four sites of Ukrainian NPPs (nuclear power plants)," Prokopchuk wrote. "However, consequences of the use of military force by the Russian federation against Ukraine will be unpredictable."

Potential backup

At least 15 countries have agreed to deploy military observers to Ukraine as early as Wednesday, responding to the country's call for assistance at the Organization for Security and Co-operation in Europe (OSCE), officials said on Tuesday. The unarmed observers will likely seek to find out more about the nature of Russia's military activities on the Crimean peninsula.

The mission comes separately from the diplomatic efforts that some OSCE countries hope to deploy, and from the contact group of key countries that Germany and others want to form as a framework for starting Ukraine-Russia talks. The OSCE also includes Russia.

In remarks Tuesday, Russia's Putin had appeared to leave little room for negotiations with Ukraine's current government: "Are today's authorities legitimate? The parliament - partially yes. All the others - no."

mkg/kms (Reuters, AFP, dpa, AP)