Russian Federation annexed Crimea in 2014 and then built a giant road bridge linking it to southern Russian Federation that straddles the Kerch Strait - a narrow stretch of water that links the Black Sea to the Sea of Azov, which is home to two of Ukraine's most important ports. Both nations called for an emergency meeting of the UN Security Council.
CBS News' Pamela Falk said the emergency meeting was called by the Russian Mission to the U.N.'s Deputy Ambassador Dmitry Polyanskiy.
"We need new sanctions against Russian Federation".
"Russia's provocative actions in the Black Sea and the Sea of Azov have crossed the line and become aggressive", the statement said.
Russia's recent actions were a violation of the United Nations' Charter as well as a violation of worldwide law, said the Ukrainian Foreign Ministry.
Recall, there is a fight, shooting: Ukrainian ships were subjected to a massive attack.
Both sides have recently increased their military presence in the Azov region, with Kyiv accusing Moscow of harassing ships heading for Ukrainian ports such as Mariupol.
According to the BBC, Ukraine alleges Russian special forces captured two of its gunboats and a tug after a chase.
Three Ukrainian crew members were injured during the altercation and subsequently received treatment from Russian medics. It said the wounded sailors were treated and their injuries are not life threatening.
Russian news agencies quoted port officials in Crimea as saying the strait was reopened to traffic early on Monday.
Moscow denies this, but admits that Russian "volunteers" are helping the rebels.
Passage through the Kerch Strait had been "temporarily blocked" by Russian ships "for security reasons" when the incident unravelled, they added.
Tensions have risen in the seas off Crimea in recent months.
But the Kyiv-based UNIAN news agency reported later that the two small-sized armored artillery boats and the tugboat did not manage to enter the Sea of Azov.
Black Sea power Turkey expressed concern on Monday while Germany said a Russian blockade of the Sea of Azov was "unacceptable".
The National Security and Defence Council of Ukraine (NSDC) has said they would support there being martial law for up to 60 days.
"In this case, you need to focus and translate the situation in a large-scale war, which is now impractical for Ukraine", he said. He said they would decide on Monday whether or not to approve martial law.
"Poroshenko did not take this kind of action during the worst of the conflict in 2014 and 2015".
Sunday's events could be created to restore Russian leader Vladimir Putin's popularity at home, which has slumped to a 10-year low due to economic woes, Russian opposition activist Alexei Navalny said.
Dramatic footage shows a Russian coast guard boat ramming a Ukrainian tugboat near the Kerch Strait Bridge.