Major US banks have sought help from the National Security Agency (NSA) to protect their computer systems following a slew of cyber attacks that disrupted their websites.

The increase in complexity of dyber attacks has prompted major banks to turn to the NSA for technical assistance in evaluating their systems and attacker strategies.

"If you look at [the government’s] actions, they’re taking this very seriously," a bank official told the Washington Post. "The government is stepping up to the plate."

US banks affected by disruptions include Bank of America, PNC Bank, Wells Fargo, Citigroup, HSBC and SunTrust.

Cyber attackers targeted about seven banks a day, but only on Tuesdays, Wednesdays and Thursdays.

The collaboration between the NSA and banks, which highlights the government’s worries regarding the unprecedented assault against the financial sector, is a part of government effort to work with US firms on cybersecurity.

In 2012, US intelligence officials said they believed that Iran carried out attacks against their banks and other firms.