(Reuters) -Toronto-Dominion Bank's handling of "suspicious" customer transactions was behind regulators' refusal to approve the lender's $13.4 billion deal to buy First Horizon, the Wall Street Journal reported on Monday, citing people familiar with the matter.

The reluctance by the Office of the Comptroller of the Currency and the Federal Reserve to give TD a clean bill of health on its anti-money-laundering practices proved to be the biggest obstacle, according to the report.

TD had pledged to regulators that it would make its anti-money-laundering policies more comprehensive and timely, but the assurances were not enough to sway regulators, the WSJ reported.

TD works to prevent criminals from using the bank for illegal activity and to strengthen its risk management programs on an ongoing basis, a spokesperson for the lender said.

First Horizon declined to comment.

The banks ended their proposed merger last week, citing a lack of clarity on when they would get regulatory approvals.

At the time, a spokesperson for First Horizon said the termination was solely related to TD and had nothing to do with ongoing banking turmoil.

(Reporting by Niket Nishant in Bengaluru; Additional reporting by Manya Saini; Editing by Maju Samuel, Anil D'Silva and Shounak Dasgupta)