UK Prime Minister Boris Johnson said on Thursday that the HMS Defender destroyer that entered Russia's territorial waters on Wednesday was acting legally in international waters.
"I think it was wholly appropriate to use international waters...The important point is that we don't recognise the Russian annexation of Crimea," Johnson told the media, according to Reuters.
Meanwhile, the Russian Foreign Ministry said that the Black Sea incident questions the relevance of the Russia-NATO act.
"Such actions call into question the relevance of the most fundamental document - the Russia-NATO act. We proceed from the fact that it must be respected, but the question cannot but arise, how, say, permanent rotation differs from the permanent presence," Russian Deputy Foreign Minister Alexander Grushko said.
The ministry also warned that anyone who carries out provocations similar to the UK HMS Defender incident, that happened on 23 June, would face dire consequences.
Earlier in the day, UK Labour Party politician Ed Miliband urged the government to explain what really happened in the Black Sea.
The Russian Ministry of Defense announced on Wednesday that the Black Sea Fleet and the border security forces had expelled the HMS Defender destroyer that entered Russia's territorial waters. While the UK Ministry of Defense rejects Russia's account of the incident, saying it was a peaceful passage and no warning shots were fired, the BBC broadcaster published a video of the destroyer entering the Black Sea that is at odds with the official statements by London.