The United States warned Tuesday that it may soon impose new sanctions on Russian figures, after Vladimir Putin laughed off the release of a US target list of his closest and richest allies.

The world was braced for a US sanctions onslaught on Monday when a new law came into effect 180 days after President Donald Trump, still hopeful for warmer ties, begrudgingly signed it.

But to general surprise, Washington declined to identify any companies or individuals to face new measures, and the Treasury contented itself with issuing a list of top Russian officials and super-rich businessmen it regards as Putin's inner circle.

Putin joked that he was upset not to have been included himself. The 65-year-old Russian president -- who is running for re-election -- said he had not seen the list and quoted an old proverb, "the dogs bark but the caravan goes on," to play down the significance of Washington's report.

However he said the US report further complicates US-Russia ties as well as international relations, but added that -- while he has "reciprocal measures" in mind -- he would take no action for now.

Later, in face Democrats grilling, Treasury Secretary Steven Mnuchin told the Senate there would be more action soon to punish Russia for human rights abuses, election interference or intervention in neighbors like Ukraine.

The list is led by Prime Minister Dmitry Medvedev, one of 114 political or official figures on the list, alongside 96 people considered "oligarchs" worth at least $1 billion (805 million euros) each, like tycoons Roman Abramovich or Oleg Deripaska.

Despite the tensions, two US sources said Russia's foreign spy chief, who is under US sanctions, met last week outside Washington with US intelligence officials.

Sergey Naryshkin, head of the Russian service known by its acronym SVR, held talks with US Director of National Intelligence Dan Coats and other US intelligence officials, the sources said. The sources did not reveal the topics discussed.