Poland says the level of Russian naval and air force activity in the Baltic Sea region has been "unprecedented" this week.
Defence Minister Tomasz Siemoniak said most of the activity was in international waters and airspace and Sweden was the country most affected.
Nato partners of the Baltic states, including the UK, have military jets on an air policing mission in the region, monitoring the Russian planes.
Fighting in Ukraine has raised tension.
Mr Siemoniak said Russia was "not preparing to attack" but it was testing Nato defences, which "does not serve to build good relationships and trust".
The three small ex-Soviet states in the Baltic - Estonia, Latvia and Lithuania - joined Nato in 2004.
Speaking on the Polish news channel TVN24, he said there was no need to put the Polish army on a state of high alert.
Nato and Ukraine accuse Russia of fomenting the conflict in eastern Ukraine and supplying the pro-Russian rebels there with troops and heavy weapons. Russia denies the allegations, but admits that Russian "volunteers" are helping the rebels.
Several incidents have been reported in the region this week:
- On Tuesday the Norwegian military said one of its warplanes had a "near miss" with a Russian fighter which had ventured too close, north of Norway
- The Finnish air force said that there had been "unusually intense" Russian activity over the Baltic Sea and the Gulf of Finland, with most flights involving bombers, fighters and transport planes heading between the Russian mainland and the Kaliningrad enclave, between Lithuania and Poland
- Nato said on Monday the alliance's jets intercepted Russian planes repeatedly in the Baltic, and reported more than 30 types of Russian military aircraft in the area
The spike in activity follows a study by the London-based think tank European Leadership Network, which detailed 40 incidents over recent months, including 11 that it said were of a "more aggressive or unusually provocative nature, bringing a higher level risk of escalation".
In one case, an SAS civilian airliner taking off from Copenhagen narrowly avoided colliding with a Russian reconnaissance plane.
Separately, Sweden conducted a massive search in October for a suspected Russian submarine in the waters near its capital Stockholm, but after a week-long hunt no submarine was found.
5 September: Abduction of an Estonian security service operative×
INCIDENT: Estonian security service operative captured by Russian agents on Estonian territory in a raid involving communications jamming and smoke grenades. Incident took place immediately after Obama’s assurances to the Baltic States.
CATEGORY: High Risk. Incursion into NATO member state’s territory. Had the Estonian official or his colleagues resisted, fatalities on either side would have been a catalyst for further escalation.
3 March: Near-collision between airliner and Russian aircraft×
INCIDENT: A commercial airline narrowly avoids collision with a Russian recon aircraft due to the latter’s not broadcasting its position.
CATEGORY: High Risk. Had a collision occurred, this would have caused a major diplomatic response, condemnation and further isolation of Russia.
June: Simulated attack by Russian aircraft on Denmark×
INCIDENT: Armed Russian aircraft approach the heavily populated Danish island of Bornholm before breaking off in what appears to have been a simulated attack.
CATEGORY: Serious. The Danish intelligence service described the incident as “of a more offensive character than observed in recent years.” At the time of the simulation, the island in question was hosting a major meeting of Danish politicians and journalists.
16 July: Provocative Russian action aimed at Swedish aircraft×
INCIDENT: Armed Russian aircraft intercepts Swedish surveillance plane conducting operations between Gotland and Latvia in international airspace, flies 10 metres from the plane.
CATEGORY: Serious. Indicated more aggressive approach by intercepting aircraft than in previous encounters.
18 July: US aircraft violates Swedish airspace to avoid Russian interceptor×
INCIDENT: American surveillance plane conducting operations near Kaliningrad takes refuge in Swedish air-space after being approached by Russian fighters. This evasive action takes place without prior Swedish approval.
CATEGORY: Serious. Indicated more aggressive approach by intercepting aircraft than in previous encounters and forced the U.S. aircraft to violate Swedish airspace.
August 2014: Multiple breaches of Finnish air-space by Russian state aircraft×
INCIDENT: Multiple breaches of Finnish air-space by Russian state aircraft.
CATEGORY: Serious. Finland has already articulated that it will respond more firmly to future violations, this is already an escalation.
17 September: Violation of Swedish airspace×
INCIDENT: Two Russian military aircraft cross into Swedish air-space south of the island of Oland.
CATEGORY: Serious. Su-24 bombers intentionally violated Swedish airspace. Swedish Foreign Minister described it as 'most serious aerial incursion' in years.
17 - 27 October: Swedish 'underwater activity' hunt×
INCIDENT: Major submarine hunt prompted by reports of “underwater activity” in Swedish territorial waters.
CATEGORY: High Risk. Biggest anti-submarine operation in Sweden since the Cold War.
28 - 30 October: Massive surge of Russian aviation activity along NATO borders×
INCIDENT: In a series of developments, aircraft from Nato states and partners track Russian long-range bombers conducting missions over the North Sea, Atlantic and the Black Sea, as well as a big formation of Russian fighter and bombers conducting missions over the Baltic Sea; all missions conducted in international airspace
CATEGORY: Serious. Large-scale Russian air operation involving different kind of aircraft and different zones of operation. While no incursion into any national airspace was reported, the operation added to increased tensions along the Nato-Russia borders.