Mobile payments startup Square is reportedly in talks for its most significant round of funding yet, which would value the company at an estimated $6bn.

Sources close to the deal have revealed that the company is near to securing $200m in investment, primarily from the Government of Singapore Investment Corp (GIC), which would boost its value up from $5bn earlier this year.

Neither Square nor the GIC have commented on the news, but the payments company is understood to be seeking extra investment ahead of a possible IPO rumoured to be happening sometime this year.

Square, which was founded in 2009 by Twitter co-founder Jack Dorsey, offers businesses a detachable card reader which lets smartphones process credit and debit card payments.

It has proved to be a significant success since its launch, attracting a range of competitors, including Amazon’s Local Register, a $10 rival service from the ecommerce giant earlier this month targeting small businesses.

The rumours come as Square announced an update to its Square Cash service, which will now let American customers send money to each other using just an email address. Users can send payments via their smartphone’s email app or via a dedicated Square Cash app, with the fund arriving in a matter of minutes.

The company says that its users have already sent millions of dollars across the US using the free app, which was originally released last year for both iOS and Android.