The Ukrainian military says it has repelled an attack by pro-Russian separatists on Donetsk airport.
Gunfire was heard from the area on September 13 despite an eight-day cease-fire between the rebels and government forces in eastern Ukraine.
Also in eastern Ukraine, a convoy of trucks which Russian officials say are carrying humanitarian aid arrived in Luhansk, the other major separatist stronghold.
The OSCE observer mission at the Russian-Ukrainian border said 220 trucks had crossed into Ukraine.
It said only 40 trucks were checked by Russian customs officials, and that none of the vehicles were inspected by the Ukrainian side or by the ICRC.
The Ukrainian government accused Russia of a "direct invasion" after a similar convoy entered Ukraine last month without permission from authorities in Kyiv.
Also on September 13, Ukrainian Prime Minister Arseniy Yatsenyuk said the Kremlin wants to “eliminate” Ukraine as an independent country.
Speaking at a conference attended by Western and Ukrainian lawmakers and businessmen in Kyiv on September 13, Yatsenyuk accused Russian President Vladimir Putin of seeking to "restore the Soviet Union."
Yatsenyuk said Putin “wants another frozen conflict" in eastern Ukraine.
He also said that despite the cease-fire to end five months of fighting in the east, Ukraine is still "in a stage of war," with the "key aggressor" being Russia.
Yatsenyuk insisted that Russia was "a threat to the global order and to the security of the entire Europe," adding that NATO was the "only vehicle" that could protect his country.
Yatsenyuk said a new wave of economic sanctions imposed on Russia by the European Union and the United States over its role in the Ukraine conflict posed a major threat to the Russian economy.
The sanctions were announced by the United States and the EU in a coordinated move on September 12 and target Russia's energy, defense, and banking sectors.
Kyiv and Western nations say there is evidence Russia is supporting the rebels in Ukraine with troops and weapons. Moscow denies this and says it will retaliate against Western sanctions.
In a reference to the latest Western sanctions, Russian Foreign Minister Sergei Lavrov accused the United States of "trying to use the crisis in Ukraine to break economic ties between the EU and Russia and force Europe to buy U.S. liquefied gas at much higher prices."
In an interview broadcast on television, Lavrov the EU was "prepared to sacrifice its economy to politics."
The Russian foreign minister also dismissed as "nonsense" claims that Russia was intent on creating a buffer zone in eastern Ukraine, insisting that that Moscow wanted Ukraine to be a "prosperous, neutral, and friendly country."
With reporting by Reuters and AFP