According to mbl.is, North Atlantic Treaty Organisation monitored the bombers, which flew nearly all the way to Spain, where they turned around and flew back to Russian Federation.
The Icelandic Foreign Ministry says that two Russianbombers of the type Tupolev Blackjack Tu-160 flew some 6 - 9 thousand feet directly underneath an Icelandic passenger plane flying from Keflavik International Airport to Stockholm.
Alexey Shadsky, a Russian diplomatic representative in Reykjavik, said the bombers complied with worldwide rules and accused Icelandic media of stoking a "Russian scare".
"It is quite understandable that this is how the matter is presented in the local papers".
Amid Russia-West tensions, the US and its North Atlantic Treaty Organisation allies have repeatedly said Russian warplanes threaten air safety.
Keflavik was used as a USA base during World War II and later in the Cold War, and Russian Federation may have fears of a return to such use after the US agreed to station some troops "occasionally", the Guardian reported. The incident occurred inside the Icelandic air traffic control area, near Norwegian air traffic control area.
"The old Russian bogey is being brought to life again", Chadisky said.
"This is global airspace so nothing illegal was going on", he added.
Other Nordic countries have made similar complaints in recent years about Russian military flights that have switched off their transponders: devices that allow radars to identify planes and prevent collisions. Media said there followed an angry reaction from Iceland's Foreign Ministry.