A former UBS trader accused of losing $2.3 billion through reckless deals and deceit broke down in tears in court Friday as he insisted he had acted purely to help save the bank he considered his family.

Kweku Adoboli denied fraudulent behavior as he took the stand for the first time, six weeks into his trial at London's Southwark Crown Court.

Prosecutors on Friday added two counts of false accounting to two similar charges and two of fraud that he already faces. He has pleaded not guilty to all charges.

Prosecutors say Adoboli lied, invented clients and breached safeguards against high-risk trading to make money for the Swiss bank and boost his bonus and status. But his off-the-book trades went wrong, and at one point he risked losing the bank $12 billion, prosecutors say.

The 32-year-old trader told a jury that he had only been trying to help UBS survive after it amassed losses of $52 billion during the 2007-2008 global financial crisis.

"There were times we thought there was no way the organization would survive," said Adoboli, who joined UBS as a trainee in 2003 and rose quickly to become a senior trader. "I grew up with UBS. I felt very loyal to UBS."

"It isn't about a bank. It was about what I thought was my family," said Adoboli, the Ghana-born son of a United Nations diplomat.

"To find yourself in Wandsworth Prison for nine months because all you did was work so hard for this bank," he said, before breaking down in tears.

Adoboli was a senior trader in exchange traded funds, which are listed and tradeable on stock exchanges and usually track a market index.

He said he and another trader, who had just 30 months of experience between them, were put in charge of a portfolio of companies with assets of $50 billion.

"Our book was massive. A tiny mistake led to huge losses. We were these two kids trying to make it work," Adoboli said.

He was arrested in September 2011 after UBS discovered irregularities in its records.

The incident was a major blow to UBS, one of the European banks hardest hit by losses from by the U.S. subprime mortgage market. The $2.3 billion loss hurt the bank's efforts to restore its image after a Swiss government bailout and a tax evasion investigation in the United States.

The trial continues.