U.S. President Barack Obama and his Republican challenger Mitt Romney on Monday sparred on the war in Afghanistan, with Obama vowing to protect U.S. troops, while Romney accusing Obama of not been forthright with voters on the situation there.

In an unscheduled press conference at the White House, Obama said he has talked with top U.S. military leaders on the recent spate of insider attacks on U.S. military personnel in Afghanistan, and will talk with Afghan President Hamid Karzai on the subject as well.

Obama, who has not spoken with the White House press corps for two months, interrupted Press Secretary Jay Carney's regular news briefing to take questions. He said the U.S. side is working on the problem of insider attacks, and the military needs to strengthen their vetting process of Afghan recruits.

Insider attacks, sometimes referred to as "green on blue" attacks, have been on the rise recently. Attackers in Afghan security forces uniforms have killed dozens international troops in 32 such attacks so far this year, posing challenge to the security transition, which would see NATO forces hand over security responsibilities to Afghan forces by the end of 2014.

Earlier in the day, Romney took to the stage in New Hampshire to answer voters' questions in a town hall meeting. He scolded Obama for not being forthcoming enough with voters and veterans about the unpopular war, and said the president needs to explain what is happening in Afghanistan.

"I expect the president of the United States to address the nation on a regular basis," said Romney.