WASHINGTON, Sept. 18 (Xinhua) -- U.S. President Donald Trump said on Tuesday that the United States is weighing the idea of establishing a permanent military base in Poland, a proposal raised by visiting Poland leader.

In a joint press conference at the White House, Poland President Andrzej Duda told reporters that he had suggested a permanent American base be set up in Poland in talks with Trump earlier in the day.

"We would call (it) Fort Trump," Duda said.

Responding to Warsaw's request, Trump said earlier that the United States was "looking at it very seriously."

"I know Poland likes the idea very much. And it's something that we are considering, yes," Trump told reporters before his meeting with Duda.

At the press conference, Trump said that the United States is reviewing the proposal from the standpoint of "military protection for both countries and also the cost."

"I think Russia has acted aggressively," Trump said, adding that Duda had offered the United States "much more than 2 billion (U.S.) dollars to do this."

"So we're looking at it," the White House host said.

Also on Tuesday, U.S. Defense Secretary James Mattis said that no decisions had been made regarding the permanent military presence in Poland.

"It's not just about a base. It's about training ranges, it's about maintenance facilities at the base, all these kinds of things," the Pentagon chief told reporters.

"So no decision's been made, we are studying it and we are working together on that," Mattis added.

Poland, a NATO member, has repeatedly required permanent presence of U.S. troops on its territory.

Moscow has voiced concern about Warsaw's intention months ago, saying NATO's expansion towards Russia's borders would destabilize Europe.