Toronto-Dominion Bank's online and mobile banking platforms in the U.S. are experiencing technical difficulties after a recent upgrade, prompting customers to complain on social media.

Several of the Canadian lender's U.S. clients have taken to Twitter to complain about problems accessing their accounts online or on the mobile app, issues which surfaced late last week after TD rolled out a technical update.

TD Bank said Wednesday it is "sorry for any inconvenience to our customers during this conversion and continue to address their questions and concerns."

It believes the challenges are either resolved or will be addressed shortly, a TD Bank spokesman added in an emailed statement.

The lender, whose slogan south of the border is "America's Most Convenient Bank," also posted a statement on its website last weekend apologizing to clients for the inconvenience.

TD Bank is one of the 10 largest banks in the U.S. and provides retail, small business and commercial banking products and services to more than nine million customers at approximately 1,300 locations.

The technical difficulties with its U.S. online and mobile platforms comes after TD's online brokerage platform WebBroker faced outages in late 2017 and earlier this year amidst an "unprecedented" surge in trading volumes.

The bank's e-transfer service also experienced some issues in November after a transition to a new platform.