Former President Jimmy Carter paid a surprise visit to President Obama while at the White House on Tuesday. 

White House press secretary Robert Gibbs told reporters during his daily press briefing that Obama invited the 39th president to "stop in" after his scheduled meeting with National Security Adviser Tom Donilon.

When asked if the meeting was regarding North Korea, where Carter has traveled to on humanitarian missions, Gibbs said he did not know.

Carter went to North Korea in July and has encouraged the U.S. to engage in direct talks with the communist nation, which carried out a missile attack on a South Korean island last week, killing four people.

In an interview with CBS News that aired Tuesday, Carter encouraged Obama to "be more independent" and not feel obligated to reach out to Republicans.

"In the next two years, President Obama will be much more independent in fighting hard to prevail and not trying to reach out, which turned out to be fruitlessly, to get two or three Republican votes for this and that," the one-term president said. "I think he'll be a much more tough proponent of what he stands for in the future, giving up on Republicans support and taking his case to the American public."