PARIS/KIEV, March 5 -- High-level diplomatic talks on the Ukraine crisis involving Russia, the United States and Ukraine failed to reach an agreement amid mounting pressure on Russia from the West.

It was difficult to reach agreements with the threats, Russian Foreign Minister Lavrov said when speaking to media after talks with U.S. Secretary of State John Kerry in Paris.

He reaffirmed Russia's position that an EU-brokered agreement signed on Feb. 21, which foresaw constitutional reform that would take into account the wishes of all Ukraine regions, should be the basis for stabilizing the situation.

Lavrov said the U.S. and Russia agreed to join efforts to help Ukraine reach the Feb. 21 agreement.

During Wednesday's talks, Lavrov did not talk to Ukrainian Foreign Minister Andriy Deshchitsya, whose new government is regarded as illegitimate by Moscow.

Also Wednesday, a top Russian legislator urged the West not to threaten sanctions against Moscow, as the potential isolation could be mutually counter-productive.

"Threats and language of sanctions towards Russia are absolutely counter-productive. It is impossible to imagine how sanctions could isolate Russia from the global economic process," Russian Federation Council (upper house of parliament) chair Valentina Matvienko told reporters.

She said the Russian economy was deeply integrated into the global economy, and trade between Russia and the West was mutually beneficial.

Noting 40 percent of Russia's imports came from the European Union, and 50 percent of its exports went to the EU, Matvienko said it was hard to imagine that these trade flows could be stopped.

She said any reasonable politician must understand the Russian and Ukrainian economies were intertwined, so Moscow could not be detached from Ukrainian affairs.

Matvienko added that if a "radical and neo-fascist plug" in Ukraine was not stopped now, other countries would soon experience the overthrow of their authorities, too.

"It's time to stop speaking to Russia with the language of ultimatums," she said, adding, only through political dialogue could it be possible to work out positive agenda for Moscow and the West.

However, NATO announced it was cutting back cooperation with Russia to try to pressure it into backing down on Ukraine.

Kerry, Deshchitsya and British Foreign Secretary William Hague on Wednesday urged Russia to honor the 1994 Budapest Memorandum.

"The Budapest Memorandum sets out the obligations of signatories in return for Ukraine giving up its nuclear weapons," they said in a joint statement during the Paris meetings.

"The Memorandum also obliges the UK, U.S. and Russia to consult in the event of a situation arising where the memorandum commitments are questioned," the statement said.

U.S. President Barack Obama spoke to British Prime Minister David Cameron about Ukraine, the White House said Wednesday.

The two leaders welcomed a military observer mission being undertaken by Organization for Security and Cooperation in Europe (OSCE) at the request of the Ukrainian government, the White House said.

The U.S. and 14 other OSCE states formed the mission Tuesday, intending to monitor the situation in Ukraine's Crimea region. The team planned to leave within 24 hours.

Obama and Cameron also discussed support for the government of Ukraine as it works to stabilize its economy and makes preparations for elections in May, the statement said, adding the leaders agreed to stay in close contact in the days ahead.

Meanwhile, a court in Kiev had issued arrest warrants for the prime minister and parliament speaker of the country's autonomous republic of Crimea, the Prosecutor General's office said Wednesday.

Criminal charges had been brought against them and other Crimean politicians, acting Prosecutor General Oleh Makhnytsky said.

Last Thursday, the regional parliament of Crimea appointed Serhiy Aksyonov, leader of the Russian Unity party, prime minister in a closed session and announced a referendum would be held over the future status of the territory on March 30.

Aksyonov said Saturday he had asked Russian President Vladimir Putin to help ensure peace in the pro-Russian region.