The Defence Forces have confirmed that four more Russian vessels, including a warship, have been observed off the Irish coast.
The presence of the military and merchant ships is the latest in a series of incidents involving Russian-registered vessels entering Irish-controlled waters.
Admiral Grigorovich, a Russian frigate, was among the vessels that entered Ireland's exclusive economic zone earlier this week.
Images taken by the Irish Navy of one of the other ships, a tanker called the Kama, appeared to show it refuelling the warship.
They were kept under surveillance by the Air Corps and Irish Navy.
In a statement, the Irish Defence Forces said the four ships were "monitored by the Irish Defence Forces during the conduct of air and naval patrols and have since departed the Irish EEZ ".
It is understood the vessels were present off the south coast of the country.
Images were taken of the commercial vessels which had entered Irish territorial waters off the Galway and Kerry coasts.
It is understood the Russian vessels observed this week were also being monitored by Britain's Royal Navy.
However, a spokesperson for the Ministry of Defence in London declined to comment other than to say "our priority will always be maintaining our national security."
The MOD spokesperson added: "That is why we increased Royal Navy presence patrols after the Nord Stream incident and have invested £65 million in the first of our two Multi-Role Ocean Surveillance ships."
Defence and security analyst Declan Power described the presence of the vessels in Irish waters, particularly a warship, as "highly suspicious activity."
While he believes there is no immediate threat to Ireland from the ships, he said Russian activity off the Irish coast must be closely watched.
He said: "It requires further depth of monitoring and analysis, and it requires us to question our resources and how we respond and how we maintain the integrity of our territory."
Mr Power like "like we do with most other things, we need to apply a multilateral approach" to the situation.
He told RTÉ News that the Russian tactic is about making its presence felt.
"It's very much about trying to influence public opinion, trying to intimidate public opinion, trying to intimidate the body politic," he added.
