They play undercover KGB spies in their hit FX show The Americans.

And Keri Russell and Matthew Rhys could have been secret agents in their suave and sophisticated evening wear as the co-stars attended a state dinner in Washington D.C on Tuesday.

Keri, 40, sported an elegant black tiered gown with gold embellishment on the bodice as she linked arms with her on and off-screen beau.

Scroll down for video

Hollywood couple: Keri Russell and Matthew Rhys made an entrance at a state dinner at the White House on Tuesday

She wore her hair in an elegant updo and wore statement gold earrings.

Some strappy black heels completed the look along with a chic clutch.

The couple made their grand entrance at the White House and greeted some of the media before heading into the dinner.

Looking the part: The actors - who plays spies in TV show The Americans - looked elegant in their evening wear as they met with members of the media

The evening was hosted by President Barack Obama to celebrate 50 years of diplomatic relations with Singapore and honoured Prime Minister Lee Hsien Loong and his wife, Ho Ching.

Matthew, 41, wore a black tuxedo suit and wore a thick beard to match his slightly unruly curly locks.

Special occasion: The couple stopped to chat before heading into the dinner in honour of Singapore's Prime Minister Lee Hsien Loong

The dinner included a mix of Washington officials and celebrities.

Keri and Matthew sat at the head table with the Obamas and Lees along with author Amy Tan, former Rep. Gabrielle Giffords, D-Ariz., and her husband, retired Navy Capt. Mark Kelly, Sam's Club President and CEO Rosalind Brewer, and Caterpillar Inc., chairman and CEO Douglas Oberhelman.

Keri and Matthew have been dating for over two years and welcomed their first child together, son Sam, in May.

Understated chic: Keri, 40, looked stunning in a black tiered gown with gold detail on the bodice

New parents: The couple have been dating for over two years and welcomed their son Sam in May

The actress already has daughter Willa, aged four, and son River, aged eight, with ex-husband Shane Deary.

In April 2014 the actors confirmed that they were indeed a couple after their relationship status had been speculated about for a year.

Meanwhile The Americans just earned the couple Emmy nominations for their portrayal of Elizabeth and Philip Jennings.

The drama also received its first Outstanding Drama Series nomination.

The couple mixed with Washington officials at the event which honoured Singapore Prime Minister Lee Hsien Loong and his wife, Ho Ching