The announcement came as Nato said that it killed 12 suspected Taliban-led fighters in an air raid in southern Afghanistan, the Associated Press reported.
The raid targeted a group of fighters riding in three pickup trucks who had opened fire on Isaf troops, Nato said.
Another battalion from the 7th Marine Regiment will make up the other 1,300 personnel.
"These marines will bring the total number of marines deployed to Afghanistan to approximately 3,600," Piper said.
The marine contingent is due to have deployed fully by the end of April, to coincide with an expected surge in Taliban-linked unrest as the weather improves.
Nato leaders have called on their partners to send more troops and equipment to fight the Taliban and their allies.
Some nations under pressure from the Taliban-led fighters in the south, particularly Canada, have threatened to leave Isaf unless they recieve support.
More than 8,000 people, most of them fighters but including 1,500 civilians, were killed in 2007 during the continuing Taliban-led insurgency, according to a UN estimate.
About 47,000 soldiers from nearly 40 nations are serving in the Isaf force, while a separate US-led coalition consists of about 20,000 soldiers, the majority American.