Defense officials in Ukraine said Tuesday there has been no letup in efforts by pro-Russia separatist fighters in the east to capture the airport in the main rebel-held city of Donetsk.
Security spokesman Andriy Lysenko said rebels fired on the terminal from tanks, artillery systems and multiple rocket launchers.
A cease-fire that nominally came into effect one month ago has been routinely flouted, with substantial shelling concentrated in the area around Donetsk airport. Fighting has also been reported in numerous other parts of the Donetsk region.
A senior U.S. diplomat visiting Ukraine called for an end on the assault on the airport, which remains under the control of government forces, and for hostilities to be suspended in other nearby towns.
In a veiled reference to Russia's widely claimed backing of separatist forces, U.S. Assistant Secretary of State Victoria Nuland demanded that foreign armed forces be pulled out of Ukraine.
"The shooting has not stopped, and the shooting must stop," Nuland told students at a university in Kiev. "All foreign forces and foreign equipment must be withdrawn."
While the airport does not bear immediate tactical significance for separatist forces devoid of any air power, the terminal's proximity to their primary stronghold is viewed as potentially undermining their longer-term security goals.
Residential buildings are frequently hit in Donetsk as a result of shelling duels. Donetsk city authorities say four civilians were killed Monday.
Rebels and government officials regularly trade accusations over who is responsible for the civilian deaths.
Separatist fighters have been observed launching artillery strikes from locations within residential areas, eliciting hasty responses from Ukrainian troops that often miss their mark and hit houses. On Tuesday, Associated Press reporters observed rebels firing weapons from the top floor of a largely deserted nine-story apartment overlooking the airport.
Rebels accuse of government forces of unwarranted and arbitrary attacks on the civilian population.
The Organization of Security and Cooperation in Europe is next week expected to come into delivery of two drones that will enable it to improve efforts to monitor violations of the Sept. 5 cease-fire agreement.
Ukrainian President Petro Poroshenko told a delegation of officials from OSCE member states Tuesday that he eventually wanted to see 1,500 observers deployed in the east and that at least 29 drones be put at their disposal.
Since unrest began, Ukraine has appealed for a broad array of foreign support, including military aid.
A convoy of 112 trucks carrying German aid destined for eastern Ukraine crossed into the country from Poland on Tuesday, the Development Ministry in Berlin said.
The aid, which was trucked to the border from 17 German cities, will be taken to a distribution center near Kiev. There, the goods will be loaded onto other trucks for the journey to cities including Kharkiv, Mariupol and Slovyansk, and items bought in Ukraine will be added. The Ukrainian Red Cross is responsible for distributing the aid, the German government said.