Gary Johnson
Gary JohnsonReuters

Libertarian presidential nominee Gary Johnson had an awkward moment during an interview on MSNBC on Thursday, when he did not know what Aleppo – Syria’s second largest city – was.

"Morning Joe" co-host Mike Barnicle asked Johnson in the interview, "What would you do if you were elected about Aleppo?"

"About?" Johnson replied.

"Aleppo," Barnicle responded.

Johnson then paused and said: "And what is Aleppo?" to which Barnicle replied, "You're kidding ...".

"No," Johnson said, prompting Barnicle to explain, "Aleppo is in Syria -- it's the epicenter of the refugee crisis.”

Johnson then offered the following response, "OK. Got it. With regard to Syria, I do think it is a mess."

Since the start of the Syrian civil war, Aleppo – which was once Syria's commercial powerhouse – has been divided between regime troops and rebels, which constantly attack one another.

On Thursday, pro-regime forces overran a strategically important district on the outskirts of the city, sealing off desperate residents in opposition-held neighborhoods.

The government advance in Ramussa has completely closed access routes into Aleppo's rebel-controlled east, under renewed siege since Sunday by forces loyal to President Bashar Al-Assad.

Up to 275,000 people in eastern Aleppo have been almost entirely cut off from food, water, medicine and electricity for over a month, while 1.5 million people living in the west of the city also face severe shortages.