KYIV, Nov 25 - Russia has fired on and seized three Ukrainian naval ships off the Crimean Peninsula in a major escalation of tensions between the two countries, Ukrainian navy reported.

Two gunboats and a tug were captured by Russian forces, while six of Ukrainian crew members were injured, according to the navy.

Ukrainian Parliament will hold an emergency session on Monday to vote on declaring martial law, Parliamentary Speaker Andriy Parubiy said.

President Petro Poroshenko, during a meeting of Ukraine's National Security and Defense Council, described the Russian actions as "unprovoked and crazy.”

The European Union called on Russia to "restore freedom of passage at the Kerch Strait" and urged "all to act with utmost restraint,” BBC reported.

NATO said it "fully supports Ukraine's sovereignty and its territorial integrity, including its navigational rights in its territorial waters.” It said Russia should "ensure unhindered access to Ukrainian ports in the Azov Sea.”

Russia has requested an emergency meeting of the UN Security Council, which US ambassador to the UN Nikki Haley says has been called for 11:00 New York time on Monday.

Tensions have recently risen in the Black Sea and the Sea of Azov off the Crimean peninsula - annexed by Russia in 2014.

The crisis began when Russia accused the Ukrainian ships of illegally entering its waters.

The Russians placed a tanker under a bridge in the Kerch Strait - the only access to the Sea of Azov, which is shared between the two countries.

Ukraine's Berdyansk and Nikopol gunboats, and the Yana Kapa tug, tried to sail from the Black Sea port of Odessa to Mariupol in the Sea of Azov.

Ukraine says the Russians tried to intercept the ships, ramming the tug. The vessels continued towards the Kerch Strait, but were prevented by the tanker.

Russia scrambled two fighter jets and two helicopters to the area. It accused the ships of illegally entering its waters and said the traffic had been suspended for security reasons.

The Ukrainian navy later said the boats had been hit and disabled as they tried to leave the area. It said six crew members had been injured.

Russia's FSB later confirmed that one of its patrol boats had used force to seize the three Ukrainian vessels but said only three sailors had been wounded.

Ukraine said it had informed the Russians of its plan to move its ships through the sea to Mariupol.

The shallow Sea of Azov lies east of Crimea, and south of the Ukrainian regions partially seized by pro-Russian separatists.

The two Ukrainian ports on its northern shore - Berdyansk and Mariupol - are key to exporting grain and produce such as steel, also for importing coal.

The 2003 treaty between Ukraine and Russia guaranteed free navigation to both countries' vessels.

But Russia has recently begun inspecting ships going to or from Ukrainian ports. Earlier this month, the EU warned it would take "targeted measures" to address the issue. (bbc/ez)