Ousted leader Viktor Yanukovych insisted on Tuesday that he remained Ukraine's legitimate president and commander-in-chief, saying he would return to Kiev and appealing to the armed forces to defy any "criminal orders" handed down by his foes.

In a defiant statement delivered in the southern city of Rostov-on-Don, Russia, Yanukovych attacked what he called the "band of ultranationalists and neo-fascists" that have replaced his government, and criticized their Western backers.

"I want to ask the patrons of these dark forces in the West: Have you gone blind? Have you forgotten what fascism is?" Yanukovych told reporters in his second such appearance since his overthrow on Feb. 22.

"I am certain the officers and soldiers of Ukraine … know what you are worth and will not carry out your criminal orders," said Yanukovych, who claims opposition forces shot police and civilians during protests against his rule last month.

Yanukovych said a May 25 presidential election would be "illegal and illegitimate" and said he would return to Kiev "as soon as circumstances allow".

"I'm sure the wait will not be long," he said.

He made his remarks after Ukraine's acting president told parliament of plans to raise a new national guard to protect against internal and external threats.

On Tuesday morning, Ukrainian parliament also warned the Crimean Assembly that it faces total dissolution if it does not call-off a referendum scheduled for March 16.

The referendum would allegedly confirm Crimea's entry into the Russian Federation or approve secession from Ukraine. There is no option on the table to remain a part of Ukraine. 

Pro-Russian authorities in Crimea closed the region's airspace to commercial flights on Tuesday in the build-up to the referendum. 

A Ukrainian plane was turned back as it tried to fly from Kiev to Simferopol. The plane was forced to return to Kiev. 

According to the captain of that flight, Crimea's airspace was closed to commercial flights on Monday, as well. Several flights from Moscow, however, were allowed to land by the armed Russian security forces currently occupying the airport in Simferopol

Russia has taken control of Ukraine's Crimea region and threatened to invade the country if it deems it necessary to protect its citizens there.

Impending EU sanctions

At a press conference in Warsaw on Tuesday morning, Polish Prime Minister Donald Tusk said that despite a stalled reaction to Russia's military intervention in Crimea, the EU will begin imposing sanctions on Russia on March 17.

"When it comes to sanctions on Russia, a decision has in fact already been made, especially on the procedure of introducing sanctions. The consequence of this will be the start of sanctions on Monday," said Tusk. 

EU governments, however, are divided about how fast, and how far to go, to punish Moscow for its military incursion into Ukraine's Crimean peninsula.

British and French diplomats told The Associated Press on Tuesday that officials are preparing a second round of sanctions on top of an initial round imposed last week. Those deemed responsible for undermining Ukrainian territorial integrity and promoting instability would suffer travel bans and frozen assets.

French Foreign Minister Laurent Fabius says these sanctions could be in place later this week. If Russia doesn't pull back from Crimea, "there is a set of sanctions that will take effect as of this week and that will consist of freezing the personal assets of Russians and Ukrainians and visa restrictions," Fabius told France-Inter radio on Tuesday.

However, the EU is likely to wait to see whether Crimea declares itself independent or is annexed by Russia before deciding on new sanctions. A vote in Crimea on Sunday could be decisive, and EU foreign ministers are scheduled to meet the next day in Brussels.

German Foreign Minister Walter Steinmeier, whose country has been more cautious than Britain and Russia's immediate neighbours, said Tuesday that the EU will decide on further sanctions by Monday if the situation doesn't improve.

NATO war exercises 

Tusk's announcement comes as NATO is set to begin a series of war games in Poland. The exercises, which include air drills over Poland and joint naval action in the Black Sea with the Bulgarian navy, as well as reconnaissance flights over Lithuana, were scheduled prior to recent events in Crimea. 

According to Polish Defence Minister Tomasz Siemoniak, the air drills were originally supposed to involve only transport aircraft, but following Russia's military intervention in Crimea, Warsaw asked that the U.S. send fighter jets instead. 

"This was our request. We really appreciate that the reaction was that quick and significant," he told reporters at a press conference on Monday at a Polish missile defence site. 

At least 12 U.S. F-16 fighter jets and about 300 military personnel are expected to arrive in Poland on Thursday morning to begin the exercises.