Russian-supported rebels launched sophisticated missiles, rockets and drones against the eastern Ukrainian city of Mariupol on Saturday, Reuters reports.
The offensive that killed at least 30 people has been called an "utter disregard of the ceasefire" by NATO Secretary-General Jens Stoltenberg.
Port city Mariupol is approximately 62 miles from the rebel-held Donetsk and offers Russia a potential land corridor to the Crimean peninsula.
Evidential of the escalating tensions in the area, Wall Street Journal reporter Yaroslav Trofimov tweeted a video showing pro-Russian rebels launching rockets in Mariupol.
Meanwhile, Russia continues to deny that troops are based in eastern Ukraine. In June, Ukrainian President Petro Poroshenko declared Mariupol as the provisional capital of the Donetsk Oblast, RFERL reports.
Analysts worry that if rebels capture Mariupol and its port, the pro-Russian separatists will have a critical logistical lifeline in the fight against Ukrainian forces.
According to government data, the sea port in Mariupol handled 13 million metric tons of cargo, making it Ukraine's fifth largest port and by far the busiest commercial marine hub on the Azov Sea, RFERL reports.
Here is a map of the area:
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