(REUTERS) - A photo of former presidential candidate Hillary Clinton glancing at a newspaper headline about US Vice-President Mike Pence using private e-mail has gone viral on social media, with thousands of people commenting on it.

Pence and others involved in the Republican presidential campaign last year criticised Clinton's use of a private e-mail server during her time as US Secretary of State.

Clinton was on an airplane travelling from Boston to New York on Friday (March 3) when a fellow passenger snapped a photo of her glancing down at Friday's USA Today newspaper front page headline "Pence used personal e-mail in office".

Pence's use of an AOL e-mail account was first reported by the Indianapolis Star on Thursday (March 2).

It said Pence used the account, which was hacked last summer, at times to discuss sensitive matters and homeland security issues while he was governor of Indiana.

Pence said on Friday he had complied with Indiana laws in his use of the e-mail account, and he had an outside attorney review his private e-mail records and archive those related to state business.

During the campaign, US President Donald Trump and Pence said Clinton's use of a private server broke the law and endangered national security - complaints that led their supporters to chant "Lock her up!" at rallies.

The State Department's internal watchdog said Clinton's use of a private server broke department rules. The FBI reviewed her e-mails for classified material, but it found that no criminal charges were warranted.