Ukraine needs to build a new international security system that should make any aggression against the country “impossible,” according to the top adviser to Ukrainian President Volodymyr Zelensky.

In a video message posted to Facebook on Tuesday, the head of Ukraine’s presidential office, Andriy Yermak, said relevant work is underway with the United States, Britain, China, Canada, France, Germany, Turkey, Italy, Poland and Israel on a “future document on security guarantees.”

“That is why I keep in touch daily with our international partners to make a new multilateral security treaty a reality,” he said, without giving details to what such a system would look like.

Peace talks: On the negotiations between Russian and Ukrainian representatives in Istanbul on Tuesday, Yermak said, “I’m sure everyone understands how difficult it is to negotiate with representatives of Russia today.”

Sanctions: A group of international and Ukrainian experts are “working daily” to analyze the sanctions imposed on Russia, he said. Ideas from a Tuesday meeting with American experts include punitive measures against the largest Russian banks and an embargo on Russian oil exports. The US has already banned Russian oil imports but an embargo would go further.

“Critical import chains will be targeted, including suppliers cooperating with the Russian military-industrial complex,” Yermak said.