US President has warned Russian leader Vladimir Putin there 'will be costs' for any incursion into Ukraine by Russian forces

The Us President issued the warning in live address at 10pm tonight (Friday), following reports coming out of Ukraine that Russia has begun an invasion into Ukraine's Crimean region.

President Obama also said he had been in contact with the Russian President daily:

13 helicopters are reported to have landed at a base near Sevestopol with 150 people on board each.

The country's acting President has urged Russian President Vladimir Putin to stop "provocations" and "naked aggression", and to pull back military forces.

Defiant Viktor Yanukovich has appeared in public for the first time since he was ousted as Ukraine's president and vowed to continue his fight for his country's future.

Speaking at a televised press conference in Rostov-on-Don in Russia, Mr. Yanukovich said he was forced out of the country by a minority of "pro-fascist thugs".

He said lawlessness and chaos had followed an agreement he signed with his opponents last Friday, which was brokered by the European Union and was intended to end three months of crisis.

He blamed the "irresponsible policies" of the West for the crisis in the country and apologised "to the Ukrainian people" for not having had more strength to endure the situation.

He made his statement as Ukraine security sources said they have regained control of two airports amid claims Russian forces tried to seize them.

Men on patrol at Sevastopol Airport in Crimea

Earlier Ukraine's interior minister Arsen Avakov accused Russian forces of staging an "armed invasion" in Crimea, something Russia has firmly denied. Commenting on the reports Mr. Yanukovych said the Crimea standoff was a natural reaction to a "bandit-like" takeover.

The accusations against Russia came after armed men were seen patrolling the perimeter at the Simferopol airport. There were also reports that Russian forces were blocking an airport in Sevastopol.

More than 10 Russian military helicopters have also flown from Russia into Ukrainian airspace over the Crimea region, the Ukrainian border guard service said.

However Ukraine's security authorities later said they had regained control of the two airports.

"There was an attempt to seize the airports, but we have localised those attempts," Ukraine's National Security and Defence Council chief Andriy Parubiy said.

"The airports are now controlled by Ukrainian law enforcement authorities".

Kiev's main airport has said that flights to the Crimean capital of Simferopol have been cancelled tonight and tomorrow morning as tensions escalate on the peninsula.

Crimean region

The Crimea peninsula has been hit by unrest over the past few days after pro-Moscow president Viktor Yanukovych was ousted and a new pro-West government was formed.

Simferopol's regional parliament was seized by separatist commandos yesterday prompting Kiev to accuse Russia of launching an "armed invasion".

The accusations come a day after dozens of pro-Moscow gunmen seized government buildings in the Crimean capital of Simferopol. These included the regional parliament, which subsequently voted to hold a referendum on May 25th to expand the region's autonomy from Kiev.

France, Germany and Poland said that they were "very worried" by events in Crimea and urged all parties to refrain from any action endangering Ukraine's territorial integrity.

Meanwhile Ukraine's acting president has dismissed the head of the country's armed forces. Admiral Yuriy Ilyin had been appointed at the height of protests against President Viktor Yanukovich, who was ousted last Saturday.

No reason was given for his dismissal in a brief statement on the presidential website. It has also emerged that Swiss prosecutors have launched a money-laundering probe against Mr Yanukovych and his son Aleksander.

Austria has also frozen the bank accounts of Mr. Yanukovych.

Ukraine will ask Russia to extradite the ousted president, the general prosecutor's office said this morning.

British Prime Minister David Cameron has had a phone conversation with President Vladimir Putin in which it is believed he warned the Russian leader not to intervene in Ukraine.

White House Spokesperson Jay Carney earlier appealed to Russia to respect Ukrainian territory.