An Instagram photo showing Ivanka Trump on vacation with Russian President Vladimir Putin's rumoured girlfriend, Wendi Murdoch, has touched off a flurry of questions on social media.

The photo, which was posted to Trump's Instagram page on Sunday, shows her standing with Murdoch in Dubrovnik, Croatia. The caption says they are sightseeing.

Another photo posted on Trump's Instagram Aug. 10 shows Murdoch posing in front of a city skyline for a Vogue Magazine modelling shoot.

"Wendi Murdoch is one of those friends that inspires you to work hard, be better and laugh louder," Trump wrote. "She is a remarkable woman whose story was beautifully told in this month's Vogue Magazine. Be sure to check it out!"

Trump and Murdoch have been friends for years, and Vogue's profile on Murdoch claims she helped Trump through a rocky patch in her relationship with husband Jared Kushner.

In March, US Weekly claimed Murdoch, 47, was dating Putin, although she denied ever meeting Putin in last month's profile in Vogue. She was previously married to British media tycoon Rupert Murdoch, the owner of News Corp and Fox News. The two divorced in 2013.

Still, the possible connection to Putin sparked a number of questions on Twitter.

Others defended Ivanka Trump's choice of company, with a few pointing out that she is also friends with Hillary Clinton's daughter, Chelsea.