SEVASTOPOL, Crimea — Masked Russian-speaking troops on Wednesday seized control of Ukrainian naval headquarters in Crimea after it was stormed by militiamen. Pro-Moscow Crimean authorities also detained the Ukrainian navy commander and reportedly blocked the defense minister and another government official from traveling to the peninsula to try to defuse tensions.

Ukraine’s military, which is heavily outnumbered in Crimea, has come under increased pressure since the region was nominally incorporated into Russia on Tuesday.

The several hundred militiamen who captured the base in Sevastopol met no resistance. Sevastopol is also the home port of Russia’s Black Sea Fleet, and tens of thousands of Russian-led troops are now patrolling Crimea.

It came a day after a confrontation between Ukrainian soldiers and pro-Russian militia left two dead.

The Russian-speaking troops, who arrived on the base after the storming, wore helmets, flak jackets and uniforms with no identifying insignia. By afternoon, they were in full control of the naval headquarters, a set of three-story boxy white concrete buildings with blue trim. It was not immediately clear how many, if any, Ukrainian servicemen remained on the base.

Ukraine’s Defense Ministry said no one was injured in the raid, which it said was led by pro-Russian militiamen and Cossacks.

The ministry said in its statement that Rear Adm. Sergei Haiduk was detained by unknown people after the storming of the fleet headquarters. The Russian state ITAR-Tass news agency reported that he was being questioned by Crimean prosecutors.

Ukraine’s defense minister and deputy prime minister had planned to travel to Crimea on Wednesday in a bid to avert an escalation in hostilities.

The prime minister in Crimea warned after the announcement of their departure that they would be turned back, however.

“They are not welcome in Crimea,” Sergei Aksyonov was quoted as saying by the Interfax news agency. “They will not be allowed to enter Crimea. They will be sent back.”

Interfax later cited Welfare Minister Lyudmila Denisova as saying the officials had been denied entry to Crimea. She said an emergency session of the National Security and Defense Council will held in response.

At the Ukrainian navy headquarters, an Associated Press photographer said the militiamen took down the gate and made their way onto the base. They then raised the Russian flag on the square by the headquarters.