Russia may be forced to sever diplomatic ties with Ukraine if there are no other options available, Russian Prime Minister Dmitry Medvedev said Friday amid the recent escalating tensions between Moscow and Kiev.

"I would not want that to happen, but if there is no other option left to impact the situation, the president could make such a decision," he was quoted by the Interfax news agency as saying.

Tensions between Russia and Ukraine have been escalating as Russian President Vladimir Putin on Wednesday accused Kiev of plotting terrorist attacks in Crimea and vowed to take additional measures to ensure the safety of the infrastructure and citizens there.

Russia has arrested a group of suspected saboteurs, two of whom admitted that they had plotted bomb attacks in Crimea upon the assignment given by the Ukrainian military intelligence service, the Interfax news agency reported Friday, citing a video footage obtained from the Russian Federal Security Bureau (FSB).

Interfax also quoted an unnamed source with Russian special services saying that one person had been arrested and several more detained, and that they had started providing testimony confirming Kiev's involvement in the terror scheme.

Ukraine has yet responded to the video footage. It was not clear when the arrests were made.

On Wednesday, the FSB said the country had prevented a series of terrorist attacks in Crimea orchestrated by the Ukraine military intelligence service, in which two Russian servicemen were killed.

Russian President Vladimir Putin said on Wednesday "the people who seized power in Kiev ... have switched to terror tactics instead of searching for ways for a peaceful settlement," calling Ukraine's actions "criminal."

However, the Ukrainian side has denied such claims.

Ukrainian President Petro Poroshenko said, "Russian accusations towards Ukraine of terrorism in occupied Crimea sound as preposterous and cynical as the statements of the Russian leadership about the absence of the Russian troops in Donbass (region of Ukraine)."

Crimea, which was previously part of Ukraine, was incorporated into Russia in 2014 following a referendum, which was recognized by Moscow but rejected by Ukraine and Western powers.

Ukrainian National Security and Defense Council Secretary Oleksandr Turchynov said the claims were "hysterical and false," and the Ukrainian Defense Ministry termed the allegations as Moscow's attempt to justify its re-deployment and actions in the region.

Ukraine will ask the UN Security Council to hold an urgent meeting if tensions continue to rise over Russia's accusations, Ukraine's Ambassador Volodymyr Yelchenko on Wednesday told reporters at UN headquarters.

RISING TENSIONS

Both sides have enhanced military readiness on the border, while the United States urged the two sides to avoid escalating tensions.

Poroshenko said on Thursday that he has ordered the country's defense and law enforcement agencies to put their units near Crimea and in eastern Ukraine on high alert.

Later Thursday, Ukrainian State Border Service's Spokesman Oleg Slobodyan said that Ukraine's frontier guards have already started enhancing the combat readiness of their units near Crimea and in the Lugansk and Donetsk regions.

In Russia, an anti-aircraft missile regiment based in Crimea has received a new S-400 Triumf air defense missile system, by far Russia's most advanced surface-to-air missile system, the Russian Defense Ministry said Friday.

The S-400 Triumf is capable of hitting an airborne target at a distance of up to 400 km with medium- and long-range missiles. The regiment will take part in a strategic command-and-staff military drill after preparations are completed, the press service of Russia's Southern Military District said.

U.S. Vice President Joe Biden spoke by phone on Friday with Poroshenko and urged him "to do his part" to avoid ratcheting up tensions with Russia, according to the White House.

Biden noted that the United States has urged the Russian side to do the same, the White House said in a statement.

Meanwhile, Ben Hodges, the commander of the U.S. Army in Europe urged Russia to allow observers, including Western journalists, to attend the upcoming military drill.

Ruslan Bortnik, head of the Ukrainian Institute of Analysis and Management of Policy, said the escalation in Crimea due to terrorist reports go against both Ukrainian and Russian interests, but help radicals and warmongers, which are not welcome by both sides.

He did not exclude possibility of foreign forces instigating trouble in Crimea.

Alexey Pushkov, chairman of the State Duma's Foreign Affairs Committee, believed that the West should impose pressure on Kiev to avoid a collapse of the Minsk agreements aimed at a peaceful settlement of the Ukraine crisis, adding Putin's warning is not only directed at Ukraine, but also at the West and the United States.

Still, analysts believed that the current situation is unlikely to evolve into a large scale military conflict.