Ukraine's acting president has said that his country was taking every possible measure to strengthen its military, as Russian forces tightened their grip on the Crimean peninsula.

Oleksander Turchinov dressed in combat fatigues praised troops taking part in exercises north of Kiev on Friday, saying they were "carrying out their duties with honour".

"Today at this training site, we saw not some sort of show, but real exercises with tank units and mobile air units essentially working in tandem," the acting head of state and commander-in-chief told the troops during the exercises, about 150km north of Kiev.

"That is the main conclusion we can make today. At the same time, we are working to strengthen our armed forces and strengthen the newly created National Guard. And I am certain that all the Ukrainian people will help us in this endeavour." 

Troops demonstrated an array of weaponry to the media, including tanks, attack helicopters and anti-aircraft and anti-tank missile systems. Similar exercises were held in other parts of the country, military officials said.

Turchinov, who took over as acting president the same day that Moscow-backed Viktor Yanukovich fled Kiev last month, said on Thursday that a build-up of Russian forces on Ukraine's eastern borders, in addition to Moscow's military takeover of Crimea, showed Russia was "ready to invade ... at any moment".

The Russian foreign minister, Sergei Lavrov, denied on Friday that the Kremlin had any plans to invade southeastern Ukraine. 

Earlier, his ministry had said Russia reserved the right to take people under its protection after clashes between demonstrators in the Russian-speaking city of Donetsk left one protester dead.

Source: Al Jazeera and agencies