Poland's ambassador to Russia has protested over assaults on two Polish diplomats in Moscow.
The latest assault happened near the Polish embassy
Ambassador Stefan Meller complained to the Russian foreign ministry following separate attacks on Wednesday on Marek Rzeszuta and Andrzej Uryadko.
Polish embassy sources said they suspected there was a political motive behind the assaults.
On Thursday evening, a Polish journalist was assaulted in Moscow in similar circumstances.
The incidents follow the mugging of three children of Russian diplomats in Warsaw on 31 July.
Russia expressed outrage over the incident, in which the teenagers were reportedly attacked by 15 youths shouting anti-Russian slogans.
The Russian foreign ministry accused Polish politicians of stirring anti-Russian feeling in the country.
On Thursday, Russia expressed "deep regret" over the assaults on the Polish diplomats, which required them to be admitted to hospital.
A Polish diplomat in Moscow, quoted by the Russian news agency RIA, said the same gang was suspected in both assaults and "we don't consider that all this was the work of hooligans".
Polish Foreign Minister Adam Rotfeld has warned that relations with Russia are getting "worse and worse".
The Polish ambassador has advised embassy staff to limit trips outside the mission's premises, the AFP news agency reports.
Pawel Reszka, Moscow correspondent for the Polish Rzeczpospolita daily newspaper, was attacked by about four men in an underground passageway near his home.
He was admitted to hospital with injuries to his head and chest.
Igor Yakovenko, general secretary of the Russian Union of Journalists (RUJ), has demanded a full investigation.
"I think that in the present case it is important for this not to lead to a further deterioration of Russian-Polish relations," Mr Yakovenko told Russian news agency Interfax.