United Airlines chief executive Jeff Smisek has resigned, following investigations into the airline's interactions with the Port Authority of New York and New Jersey (PANYNJ).

Oscar Munoz replaces Smisek as president and chief executive of the Chicago-based carrier effective immediately, the airline says. He was previously president and chief operating officer of CSX.

"It is truly a privilege to serve as United's CEO,” says Munoz in a statement. “United has an incredible opportunity for improving an experience that is essential to the vitality of global business and to the personal lives of millions of people, for innovation, and for earnings growth.”

Munoz already serves on United’s board of directors.

Smisek’s departure comes as US authorities continue to investigate the PANYNJ, which operates Newark Liberty International airport. United says his departure, as well as those of two other executives, are connected to the internal investigation it mounted as part of the federal probe into the Port Authority.

Both the internal and federal investigations continue, the carrier says.

The investigation reportedly stems from a 2011 dinner attended by Smisek and then PANYNJ chairman David Samson where the Port Authority chief jokingly asked Smisek to resume service between Newark and Columbia, South Carolina, reported Bloomberg in April. Columbia is near a weekend home owned by Samson.

Smisek was pushing the PANYNJ for a commitment to extend the PATH commuter train to Newark airport, the media outlet reports.

United began Newark-Columbia service in 2012 only to discontinue it after Samson resigned in March 2014.

Irene Foxhall, executive vice-president of communications and government affairs, and Mark Anderson, senior vice-president of corporate and government affairs, have also resigned.

Smisek has been chief executive of United since 2010, where he oversaw its merger with Continental Airlines. He was previously Continental's chief executive, having joined that airline in 1995.

Source: Cirium Dashboard