NEW YORK - Hillary Rodham Clinton's silence on the e-mail controversy swirling around her is getting louder by the day.

On Monday, the potential 2016 Democratic presidential candidate ignored the issue at a forum while a second Democratic senator urged her to speak out - and predicted she will - about her decision to conduct business while secretary of state in a private e-mail account. Republicans are ramping up their attention on the issue.

At the White House, spokesman Josh Earnest said President Obama indeed knew she was using a nongovernment account during her tenure. Obama had indicated earlier that he only learned of that from recent news reports.

Earnest said the president actually learned from those news reports of Clinton's privately run e-mail server, but was familiar with her private account earlier because the two had exchanged e-mails when she was in office. Obama did not know at the time that she was using private e-mail exclusively, Earnest said.

Clinton spoke at a carefully choreographed two-hour event involving her No Ceilings project at the Clinton Foundation, highlighting economic and educational opportunities for women and girls. She took no questions.

Clinton is under scrutiny over whether she fully complied with federal laws requiring government officials to preserve written communications involving official business. Democrats have defended her, but Democratic Sen. Dianne Feinstein of California made waves Sunday when she urged Clinton to offer a detailed explanation. "From this point on, the silence is going to hurt her," Feinstein said.

On Monday, Sen. Amy Klobuchar (D., Minn.) said Clinton will probably address the matter - and should. "I think that you're going to hear something from Secretary Clinton this week," she said on MSNBC. "I'm fairly certain it will be soon. I think that's very important."

Last week, Clinton said that she wanted her e-mails released by the State Department as soon as possible - but did not address why she does not put them out herself immediately.