The SBU claimed that the organisation aimed to “take advantage of the tense political situation in Ukraine and discredit our state in the international arena.”
They added that the group received funding from Russian military intelligence totalling more than $10m.
The SBU also alleged that Mr Dubinsky was being guided by GRU to spread fake news about Ukraine’s military and political leadership, including claims that high-ranking Ukrainian officials were interfering in US presidential elections.
The SBU did not name the suspect, but lawmaker Yaroslav Yurchyshyn, first deputy head of the parliamentary committee on anti-corruption policy and lawmaker Oleksiy Honcharenko both named Mr Dubinsky in statements posted to the Telegram messaging app.
“Dubinsky received a (notice of) suspicion of state treason. He was searched today,” Mr Honcharenko said.
Mr Dubinsky has denied any wrongdoing, calling the investigation “political persecution” in a statement posted to Telegram. He added that the charges are fabricated and “based on the absolute lies of top state officials”.
If convicted, he could face up to 15 years in prison and he would be forced to forfeit his assets. He is being held without bail until further proceedings on 12 January 2024, Suspilne media reported.
Mr Dubinsky was previously sanctioned by the US after he gave several press conferences in Kyiv in 2019 in which he claimed he was aware of corruption and money-laundering schemes related to Burisma, a gas company which had Mr Biden’s son Hunter on its board of directors. He also claimed US investment funds were involved in money laundering in Ukraine.
The MP was expelled from the ruling Servant of the People party as a result of being sanctioned, but he continued to work in parliament and denied all the accusations against him.
Ex-Ukrainian lawmaker Andriy Derkach and ex-prosecutor Kostyantyn Kulyk were also involved in the press conferences.
Both men were accused of being part of the group alongside Mr Dubinsky, which the SBU claims is run by GRU deputy head Vladimir Alekseyev and his deputy Oleksiy Savin, and charged with treason.
Mr Derkach and Mr Kulyk are now in hiding abroad and have been sanctioned by the US.
It comes after Mr Giuliani travelled to Kviv in December 2019 to film a documentary aimed at discrediting an impeachment probe into the former president.
During his visit, he met with Mr Dubinsky and Mr Derkach, who then announced they would be setting up a new cross-party “anti-corruption” group with Mr Giuliani’s help.
An impeachment inquiry into Mr Trump’s shadow diplomacy in Ukraine was later launched by Congress to which evidence was presented suggesting Mr Giuiliani pushed discredited conspiracy theories involving Ukraine to boost his boss’s election prospects.
He is also cited as a driving force behind lobbying Ukraine’s president Volodymyr Zelensky to open a criminal investigation into the family of Trump’s major rival Joe Biden.