Sikorski met Belarusian Foreign Minister Maksym Ryzhenkov in New York on Tuesday on the sidelines of the UN General Assembly.
The talks focused on the situation on the Polish-Belarusian border and regional security.
"Breakthrough is too strong a word, although it is the first meeting in about a decade," Sikorski told a press briefing at the United Nations on Wednesday.
"I called it a snowdrop yesterday. The Belarusian side replied that it wants a harvest, so there is evidently a willingness to unfreeze relations," he added, while cautioning that Warsaw was "not nurturing vain hopes."
Sikorski said Minsk had changed its approach because "the facts had changed."
Warsaw had demanded the release of political prisoners, including Polish-Belarusian journalist and activist Andrzej Poczobut, and Belarus had complied, he said.
"There is an opening, and it is not known where it will lead," Sikorski said. "We have no illusions, but in general it is better to live well with one's neighbours than badly, and better for Belarus to be an independent state pursuing its own policy."
Poczobut, a journalist and prominent member of Belarus' Polish minority, was released in April as part of a prisoner exchange after more than five years of detention.
Sikorski's talks with Ryzhenkov also covered the case of Polish soldier Sgt. Mateusz Sitka, who was stabbed to death on the border.
Sikorski said Belarus had assured him it would provide legal assistance if Poland asked again, although it had made a similar pledge before.
He declined to give details, calling it a "very delicate process."
Sikorski said the border was calm, with no successful crossings from Belarus since the start of the year.
He credited a barrier begun by the previous government and completed and reinforced under Prime Minister Donald Tusk's administration.
"This is not Belarus' merit, but the result of our spending of almost EUR 1 billion, but a fact is a fact," Sikorski said.
Sikorski said he had briefed the Belarusian opposition, whose leader lives in Poland, and that its representatives appreciated the notice.
He described a remark by opposition figure Pavel Latushka, who said he hoped the fate of Belarusians would not be decided behind their backs, as "an expression of concern" rather than a protest.
"By their fruits you shall know them," Sikorski concluded.
(jh/gs)
Source: PAP