Russia has reaffirmed its pledge to “respect the territorial integrity of Ukraine”, despite placing fighter jets on combat alert along the countries’ shared border.

The pledge came after US Secretary of State John Kerry spoke to Russian Foreign Minister Sergei Lavrov amid ongoing tension in Ukraine.

Mr Kerry sought assurances from Mr Lavrov that Russia would work with the United States to create unity in Ukraine.

“I asked specifically that Russia work with the United States and our friends and allies in order to support Ukraine to rebuild unity, security and a healthy economy,” Mr Kerry told reporters.

Mr Lavrov reaffirmed President Vladimir Putin’s statement that Russia “will respect the territorial integrity of Ukraine,” Mr Kerry added.

Mr Kerry called on Russia to work with the US

Mr Lavrov also denied that Moscow had any hand in the takeover of government buildings in the Crimea, over which a Russian flag was hoisted on Thursday.

There are reports that armed men are also patrolling the grounds of Simferopol Airport in the Crimea.

The White House has reinforced its warnings to Russia that it must avoid “miscalculations” in military drills along the border of Ukraine.

The comments appeared to reflect Washington’s concern that Russian manoeuvres near the ex-Soviet state could trigger events which may get out of control.

Mr Kerry said his Russian counterpart had assured him that the exercises were long-planned and had nothing to do with the fast-moving events in Ukraine.

The parliament building has been seized in Simferopol

Ousted Ukrainian President Viktor Yanukovych has reportedly announced that he will hold a press conference today in the southern Russian city of Rostov-on-Don.

Mr Yanukovych has reportedly been spotted in a luxury five-star hotel and spa outside Moscow, in an exclusive enclave favoured by Russia’s super-rich.

The 63-year-old fugitive, who is wanted in Ukraine on charges of mass murder after police opened fire on demonstrators, released a statement on Thursday insisting he is still president.

Mr Yanukovych and his government are facing charges of stripping Ukraine’s coffers bare before they were toppled from power.

Mr Lavrov says Russia will respect Ukraine’s territorial integrity

Shortly before being appointed as head of the crisis-hit country’s national unity government, Arseny Yatseniuk said $37bn (£22bn) had disappeared in an “unknown direction”, while $70bn (£42bn) had been siphoned out of the economy into offshore accounts.

But Russia has questioned the legitimacy of the new Ukrainian authorities and has pledged to defend the rights of its “compatriots”.

Crimea’s parliament, which is currently being controlled by pro-Russian gunmen, has voted to hold a referendum on May 25 on the region’s status.

A raid on the region’s capital of Simferopol saw up to 50 men in combat fatigues storm the official buildings, erect barricades, and put up signs saying “Crimea is Russian”.

Crimea is an autonomous republic in the south of Ukraine, around 500 miles from the capital Kiev.

There have been mounting signs of separatism in the region, which has strong ties to Moscow and where the majority of the population are Russian speakers.