A convoy of Russian military equipment, including at least three missile launchers, has crossed into Ukraine, according to officials in Kiev, as a fighter jet was shot down by pro-Moscow rebels.
A Ukrainian military spokesman said at least three Grad missile systems were among the weapons being sent to the separatists in the east of the country, who are battling a Ukrainian government offensive.
"We have information that rebels used their routes, which are not under control by Ukrainian army, and got some ammunition and troops that crossed from the Russian Federation," Andriy Lysenko said.
"We can't the say exact number of them, we're checking this information."
Russian vehicles with containers for BUK-M1 missiles in Rostov on Saturday He also told journalists that Russian drones had violated Ukrainian air space on 10 occasions.
A spokesman for Russian President Vladimir Putin denied Sunday claims that the separatists had received weapons or armoured vehicles.
"We have repeatedly said that no equipment is being sent there," Kremlin spokesman Dmitry Peskov told Govorit Moskva radio.
The fighter jet MiG-29 plane was shot down in the Luhansk area, where Ukrainian forces recaptured a police station on Sunday after more than three months under the control of the separatists.
The plane was shot down in the Luhansk region of eastern Ukraine The pilot ejected from the MiG-29 plane and has been found after a search, spokesman Oleksiy Dmytrashkivsky said.
Mr Dmytrashkivsky said the plane was shot after launching an attack on rebels.
The shooting down of the plane came after Kiev and Moscow reached agreement on the passage of a Russian aid convoy into the east.
There are reports that 16 of the aid trucks left the parking lot in western Russia where the convoy has been waiting and headed for the Ukrainian border, however they were not expected to cross on Sunday.
Several lorries from a Russian aid convoy are moving to the border Ukraine had been concerned the convoy of 280 white trucks could be a 'Trojan horse', allowing Russia to set up a permanent presence in rebel-held territory.
But Russia "guaranteed" the US that no military personnel were in the vehicles, which have been stuck near the border for the past few days.
Moscow says the trucks are carrying water, food and medicine for people displaced by fighting in eastern Ukraine.
Red Cross officials have been examining the contents of the lorries.
They say they need security guarantees from both sides before the convoy can start moving across the border.
Fighting in Ukraine has escalated since the insurgency arose in April, with government troops steadily taking back rebel-held territory in the east.
Luhansk is reportedly suffering from severe electrical outages and shortages of food and medicine.
Donetsk, the largest rebel-held city, is also suffering through frequent shelling.
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