Sergei Kislyak, Russia's then Ambassador to the United States, arrives for a Donald Trump for President campaign event at the Mayflower Hotel in Washington, April 27, 2016. (Reuters Photo)

MOSCOW, Aug. 5 (Xinhua) -- Former Russian Ambassador to the United States Sergey Kislyak said Saturday that he only touched upon "very simple things" with former U.S. National Security Adviser Michael Flynn in a December conversation that finally led to the latter's resignation.

In a news program on the Rossiya 24 TV channel, Kislyak said Moscow had instructed him not to discuss the U.S. sanctions with anyone since they were illegal and he had strictly followed the instruction.

"There were no secrets from our side," he said, stressing that the conversation was transparent and appropriate.

Flynn, the first national security adviser of U.S. President Donald Trump, resigned in February amid rampant reports that he had lied about improperly discussing U.S. sanctions on Russia imposed by the Obama administration with Kislyak weeks before Trump's inauguration.

Flynn has acknowledged that he spoke to the Russian ambassador but denied discussing the sanctions.

Kislyak said he would not testify before the U.S. Congress if invited amid the ongoing investigation into the Trump administration's alleged collusion with the Russian government.

As for Moscow-Washington relations, he said there is not yet a new Cold War, but the current trend in bilateral ties will continue for a long time.

Kislyak returned to Russia last month after serving as the Russian envoy to the United States for nine years. A new ambassador has yet to be appointed.