WASHINGTON, July 27 (CGTN) -- The White House on Friday said Donald Trump was open to the idea of visiting Moscow after Vladimir Putin revealed he had invited the US president.

On the sidelines of the 10th BRICS Summit in Johannesburg, the Russian President told reporters that he had invited Trump to visit Moscow. He also said that "I am ready to go to Washington."

Putin made this announcement after the US administration earlier this week delayed a second summit between him and Trump to next year under fire from critics within the US.

The White House responded with a statement saying "President Trump looks forward to having President Putin to Washington after the first of the year, and he is open to visiting Moscow upon receiving a formal invitation."

"Face-to-face contacts needed"

He said talks should begin on the possible extension of a nuclear arms treaty which was signed by Trump and Putin's predecessors, Barack Obama and Dmitry Medvedev in 2010 and which will expire in 2021.

"Are we going to extend it or not?" he asked. "Contacts at the highest political level are needed," Putin said. "You cannot discuss everything by phone."

Separately, US Secretary of Defense Jim Mattis said he was considering the possibility of the first talks in years between the defense chiefs of the United States and Russia.

Mattis said there had been no decision.

All about the 2016 election

The summit between the US and Russian leaders in Helsinki this month unleashed political turmoil in Washington, with some critics accusing the US president of betraying America's interests.

Trump faced particularly intense criticism after the news conference, during which he appeared to support Putin's "extremely strong and powerful" denial of alleged Russian meddling in the 2016 US presidential election.

In the meantime, Trump on Friday denied knowing in advance about a 2016 meeting his son Donald Trump Jr. and other campaign staff had at Trump Tower with a group of Russians who offered damaging information on Clinton.

The Russian president said the two leaders needed to see each other face-to-face to discuss a host of bilateral and international issues like Syria, Iran and nuclear arms control.

A CNN report said his longtime lawyer Michael Cohen planned to tell special counsel Robert Mueller, who is investigating the Russian interference in the election, that Trump did know of the meeting.