Washington: Russian President Vladimir Putin's gift of a soccer ball to US President Donald Trump last week set off a chorus of warnings - some of them only half in jest - that the World Cup souvenir could be bugged.

Republican Senator Lindsey Graham of South Carolina even tweeted: "I'd check the soccer ball for listening devices and never allow it in the White House".

It turns out they weren't entirely wrong. Markings on the ball indicate that it contains a chip with a tiny antenna that transmits to nearby mobile phones.

But rather than a spy device, the chip is an advertised feature of the Adidas AG ball. Photographs from the news conference in Helsinki, where Putin handed the ball to Trump, show it bore a logo for a near-field communication (NFC) tag. During manufacturing, the NFC chip is placed inside the ball under that logo, which resembles the icon for a Wi-Fi signal, according to the Adidas website.