NEW YORK — Two former JPMorgan Chase & Co. traders were accused of trying to conceal the size of the investment bank’s $6 billion trading loss last year in criminal conspiracy charges unsealed today that raised fresh questions about whether Wall Street learned its lessons from the 2008 financial crisis.

Javier Martin-Artajo, 49, and Julien Grout, 35, and their co-conspirators were accused of “artificially increasing the market value of securities to hide the true extent of hundreds of millions of dollars of losses,” according to court papers.

The case is related to a surprise loss last year by trader Bruno Iksil, who became known as the “London whale” for the supersized bets he made. Martin-Artajo, who supervised JPMorgan’s trading strategy in London, and his subordinate Grout, who recorded the value of the bad investments, are accused of conspiring to hide more than a half-billion dollars of losses in a trading portfolio that ultimately lost more than $6 billion.

Martin-Artajo and Grout were charged in federal criminal complaints with conspiracy to falsify books and records, commit wire fraud and falsify Securities and Exchange Commission filings.