U.S. Presidential National Security Aide Jake Sullivan has held a series of confidential contacts in recent months with Russian presidential aide Yuri Ushakov and Russian Security Council Secretary Nikolai Patrushev on the unacceptability of nuclear weapons and expanding conflict in Ukraine, The Wall Street Journal reported, citing U.S. and Western officials.

The purpose of the contacts was to prevent escalation and preserve channels of communication, not a settlement in Ukraine, the newspaper points out.

The newspaper's sources did not specify exactly when the contacts took place or how many there were. Sullivan's press service did not confirm their fact. Earlier, Sullivan said that the US had warned Russia at a high level against the use of nuclear weapons in Ukraine, but he did not specify with whom exactly in Moscow the conversation took place.

The Wall Street Journal called Sullivan a supporter of maintaining channels of communication with Moscow, which some other administration officials oppose.