Russia's newest attacks come as its Ministry of Defense is moving forward with the purchase of at least 10 unmanned underwater vehicles.
Kremlin spokesman Dmitry Peskov said "it is only possible to welcome" a U.S. move to extend the arms reduction treaty, which expires on February 5.
The Royal Navy's HMS Mersey and HMS Tyne joined NATO ships to escort the Russian vessels.
Tensions with NATO are high in the Baltic Sea and Nikolai Yevmenov said in a message that six Karakurt-class corvettes would boost Russia's fleet there.
The treasury secretary also told a London event that the U.S. is "prepared to dedicate a lot of resources" to a U.K. trade deal.
Experts warn that as well as Brexit, Iran is the first major foreign policy problem for Johnson, whom the U.S. president has lavishly praised.
Majorities of people in eight countries think immigration from mainly Muslim countries should be stopped.
A Chatham House report says shifting to a plant-based diet could drastically lower global greenhouse gas emissions.
The instinctive response is to bomb ISIS, but improving local governance will be more effective
A new report suggests that some facilities could be hacked using "nothing more than a flash drive."