The continued conflict in Afghanistan will be a key topic at the Nato summit.
More than 8,000 people died in Afghanistan last year, making it the most violent year since 2001, when the US invaded the country to oust the Taliban-led government after the September 11 attacks in 2001.
Nato has about 43,000 troops in Afghanistan, but commanders have asked for more in areas of southern Afghanistan where troops stationed there continued to battle Taliban fighters.
The US contributes one-third of the Nato force, and also has about 12,000 other US troops operating independently from Nato.
According to the Pentagon, there will be about 32,000 US troops in Afghanistan by late summer.There are currently 28,000 troops in the country.
The bulk of the increase includes the deployment of 3,600-strong marine contingent.
They arrived on Tuesday and will be commanded by the Nato-led International Security Assistance Force (Isaf), and not by a separate US-led force.