Russia's ambassador to Poland, Sergey Andreyev, has said he meant no offence when he appeared to suggest Poland was partly to blame for the start of World War Two.
Ties have sharply deteriorated in recent years, and the government in Warsaw has sharply criticised Russia's conduct in Ukraine.
But Mr Andreyev's interpretation of history brought relations to a new low.
He told reporters his remarks had not been "sufficiently precise".
The ambassador was speaking outside the Polish foreign ministry, after he was summoned over his comments on Polish TV channel TVN24 on Friday.
However, his comments to Russian media later made clear that there was unlikely to be any immediate improvement in relations.
"I am not retracting my remarks, I am simply making a clarification because they were misinterpreted," he said, adamant that he was referring not to the start of the war but to the catastrophe in Poland. There had been no discussion about his possible expulsion from Poland, he added.
A Polish official said that during the meeting it was noted that the envoy's remarks had been "untrue and contrary to the findings of Polish and Russian historians". He said the Russian parliament itself had in 2010 directly blamed Soviet dictator Josef Stalin for ordering the 1940 massacre of 20,000 Polish prisoners of war at Katyn.
Mr Andreyev had argued that Poland was partly responsible for what happened in September 1939, because "during the 1930s Poland repeatedly blocked the formation of a coalition against Hitler's Germany".
The war erupted in September 1939 when Nazi Germany invaded Poland from the west, little over a week after the USSR and Germany signed the Molotov-Ribbentrop pact. Soviet forces entered Poland from the east that same month, as part of the secret agreement.
Mr Andreyev had also suggested that the Soviet invasion was "to ensure the safety of the USSR" and was not an aggressive act.
Polish Prime Minister Ewa Kopacz pointed out at the weekend that "even children in Poland know that neither Ribbentrop nor Molotov was Polish", condemning the Nazi-Soviet carve-up of her country.
The ambassador's interview on Friday was broadcast hours after Poland's ambassador to Moscow, Katarzyna Pelczynska-Nalecz, was herself summoned to the Russian foreign ministry because the graves of 57 Soviet soldiers were vandalised at a cemetery in Milejczyce in north-eastern Poland. The vandalism was strongly condemned by the Polish government.
Russia is also angry that Polish officials this month removed a brass relief of a wartime Soviet general, Ivan Chernyakhovsky, from a monument in northern Poland.