Ukraine's U.N. ambassador says a convoy of Russian tanks and armored vehicles has moved from the resort town of Novoazovsk toward the key port of Mariupol and was stopped by Ukrainian forces and civilians.

Yuriy Sergeyev told a news conference that the convoy started moving Thursday morning and "the fight is still going on right now."

He said the convoy from Novoazovsk, which was captured by heavily armed Russian-backed separatists last week, had four tanks, three armored vehicles and about 50 soldiers, and "most probably" was a reconnaissance mission to test Mariupol's military defenses.

Novoazovsk lies along the road linking Russia to Mariupol and onto Crimea, the Black Sea peninsula that Russia annexed in March.

Sergeyev said Russia is "most probably" trying to build a land corridor to Crimea.