Credit Suisse began its defence in a Singapore court on Monday against a lawsuit filed by former Georgian Prime Minister Bidzina Ivanishvili alleging the bank's local trust did not properly protect his family's investments, leading to losses.

Ivanishvili has accused Credit Suisse Trust Ltd in Singapore of not meeting its duties to "safeguard the assets and take the appropriate steps" to prevent losses linked to fraud committed by the bank's former Geneva-based banker Patrice Lescaudron.

The latest court case comes as the Swiss bank's new chief executive Ulrich Koerner is seeking to put the bank back on an even keel after a string of scandals.

In a statement read to the court on Monday, Ivanishvili's barrister Cavinder Bull SC said $1.1 billion had been placed under the custodianship of the Credit Suisse Trust in 2005.

Lescaudron was the Credit Suisse "conduit" for Ivanishvili's business and started "fraudulently mismanaging" the trust's investments and "misappropriating" the trust funds as early as 2007, Bull's statement said.

Ivanishvili calculated his loss as $1.27 billion, while the trustee said it stood at $818.2 million, the statement said.

Lescaudron was convicted by a Swiss court in 2018 of forging the signatures of former clients, including Ivanishvili, over an eight year period. He admitted he falsified trades and hid losses as part of a scheme that made him tens of millions of Swiss francs.

Lescaudron subsequently took his own life, court documents said.

In its opening statement, Credit Suisse said the proceedings against the bank were "overreaching".

The bank said Credit Suisse Trust accepted it was "under a duty to protect the Trust Assets if it had actual knowledge that those assets were not being managed properly". However, at that time it did not have such knowledge, it said.

"CS Trust invites the Court to dismiss the claim as being against the wrong defendant and on the wrong basis," it said.

Ivanishvili gave evidence to the court via video link on Monday.

The hearing before Justice Patricia Bergin continues.