"We can't help paying attention to the North Korean nuclear issue," Hwang Jin-ha, a member of the conservative opposition Grand National Party, told parliament before the vote.
He said closer cooperation with the US was crucial as North Korea threatened to slow its disabling of nuclear facilities due to delayed aid.
South Korea has 650 troops stationed in Iraq for a reconstruction mission since 2003 at the request of Washington.
The US has 28,000 troops based in South Korea as a deterrent against North Korea.
The South's troops level once stood at 3,600, making it the largest US largest coalition partner after Britain.
However, Seoul has gradually brought soldiers home due to anti-deployment sentiments that peaked when a South Korean civilian working in Iraq was kidnapped and beheaded in 2004.