U.S. Defense Secretary Jim Mattis has expressed concern over Russia's activities in Afghanistan and its interaction with the Taliban militant group.
"We have seen Russian activity vis-a-vis the Taliban," Mattis said during a news conference in London on March 31.
"I am not willing to say at this point if that is manifested into weapons and that sort of thing, but, certainly, what they are up to there in light of their other activities gives us concern," he added.
The comments come after U.S. General Curtis Scaparrotti, NATO's supreme allied commander in Europe, told a U.S. Senate committee on March 23 that he had seen evidence of increasing Russian efforts to influence the Taliban "and perhaps even to supply" the militant group.
Moscow denies it provides aid to the Taliban, which is fighting the U.S.-backed government and U.S. forces in Afghanistan.
Mattis also said in London that Iran continued to be an "exporter of terrorism" and a sponsor of militant activity.
He said Iran's behavior had not changed since 2012, when he said the three primary threats the United States faced were "Iran, Iran, Iran."
"At the time when I spoke about Iran I was a commander of U.S. Central Command and that [Iran] was the primary exporter of terrorism, frankly, it was the primary state sponsor of terrorism and it continues that kind of behavior today," he said at a news conference with his British counterpart, Michael Fallon.
Mattis also said that North Korea was acting "in a very reckless manner" and "has got to be stopped," an apparent reference to Pyongyang's nuclear weapons and missile programs.
"This is a threat of both rhetoric and growing capability," he said.