An Afghan soldier carried out an insider attack on American forces in northern Afghanistan, according to U.S. and Afghan officials.

It's the second insider attack, known in the military as "green-on-blue," of the month. Three U.S. soldiers were killed last week by an Afghan soldier who was supposed to be their partner in an attack claimed as a victory for the Taliban.

"At this time we can confirm there are no U.S. or NATO Resolute Support fatalities," the Defense Department said in a tweet. "Seven U.S. service members wounded, evacuated for treatment," it said in a follow-up statement.

The DOD statement contradicts an Afghan military spokesman's casualty report. "An Afghan soldier shot and killed four American troops inside the base," Abdul Qahar Araam, spokesman for the Afghan Army's 209th Corps, told Reuters.

The Defense Department also said one Afghan soldier was killed and another wounded in the attack.

Camp Shaheen, the location of Saturday's attack, has been a recurring target of the Taliban. In April, about 140 Afghan soldiers were killed when ten Taliban fighters infiltrated the base during prayers and launched a surprise attack. The Taliban "claimed that four of the attackers were soldiers who had served at the base and had knowledge of the facility," according to Al Jazeera.

The latest green-on-blue attack comes as Defense Secretary Jim Mattis is considering asking President Trump to deploy more U.S. forces to the country, to prevent the Islamic State and the Taliban from further destabilizing the country.

"We are not winning in Afghanistan right now, and we will correct this as soon possible," Mattis told the Senate Armed Services Committee on Tuesday.

The new policy could involve 3,000 to 5,000 additional American forces to train Afghans, while U.S. officials also increase pressure on Pakistan to stop allowing terrorist forces fighting to operate out of the region bordering Afghanistan. "We're going to have to look at a more regional strategy, one that takes into account Afghanistan as part of South Asia, not look at it in isolation," Mattis said.