Warning shots were fired when pro-Russian forces refused entry to Crimea of an international monitoring team from the Organization for Security and Cooperation in Europe.
It was the third day in a row that a team of observers has been refused entry to the area.
The OSCE said via Twitter that the team would return to the southern Ukraine city of Kherson.
Meanwhile, a convoy of military vehicles, apparently Russian, has entered a base near Crimea's capital Simferopol.
Reuters news service, which filmed the vehicles and identified them as Russian, said the convoy included eight armored vehicles, two ambulances and gasoline tankers.
The Associated Press said the vehicles traveled to a military airfield over which a Russian flag flew.
Russia has denied it has troops in Crimea beyond those regularly stationed with its Black Sea fleet, which is based in Crimea.