Russia will respond if its interests are attacked in Ukraine, as they were in South Ossetia in 2008 which led to war with Georgia, Foreign Minister Sergei Lavrov said today.
"If we are attacked, we would certainly respond," he told state-controlled RT television in an interview.
"If our interests, our legitimate interests, the interests of Russians have been attacked directly, like they were in South Ossetia for example, I do not see any other way but to respond in full accordance with international law."
Lavrov did not elaborate further on what the response would entail but the reference to Georgia's breakaway region of South Ossetia hints at the possibility of military action.
In August 2008 Russia sent troops into South Ossetia and then into Tbilisi-controlled Georgian territory after then president Mikheil Saakashvili tried to reestablish control over the breakaway region.
Russia then recognised South Ossetia and another breakaway Georgian region, Abkhazia, as independent in defiance of the West.
"Russian citizens being attacked is an attack against the Russian Federation," Lavrov told RT, which published excerpts of the English-language interview to be broadcast later today.
The West has accused Russia of clustering thousands of troops around Ukraine's eastern forces and of already sending special forces into the country. Lavrov however strongly denied that any Russian forces had entered Ukraine.
"The only thing I would like to highlight at this stage is that the Russian troops are on the Russian territory."
He added that this had been confirmed by international inspections involving Ukraine, Europe and the United States.
"No one who participated in these inspections... ever brought up any fact that would indicate Russia was engaged in some dangerous military activity," said Lavrov.
The West has strongly warned Russia against sending troops into eastern Ukraine to aid pro-Moscow separatists. President Vladimir Putin has said he hopes there will be no military action but has not ruled out such a move.
Lavrov also accused the United States of controlling the actions of the pro-West Ukrainian government, saying that Washington was now "running the show" in Kiev.
He noted that Ukraine had chosen to relaunch military operations against separatists in the east during a visit to Kiev by US Vice President Joe Biden.
"There is no reason not to believe that the Americans are running the show in the most direct way," Lavrov said.
Relations between Russia and the West have dived to a post-Cold War low after the February ousting of president Viktor Yanukovych which Moscow denounced as an illegal takeover of power.