World leaders are meeting with President Obama in his hometown of Chicago for a two-day NATO summit focused heavily on Afghanistan. 

Obama warned of the difficulty ahead as the summit confronted questions about Afghanistan's future. The summit kicked off on Sunday with a meeting between Obama and Afghanistan's President Hamid Karzai, the two key players to determine that future. 

"We still have a lot of work to do and there will be great challenges ahead," Obama said. "The loss of life continues in Afghanistan and there will be hard days ahead." 

Reporting from Chicago, NPR's Jacki Northam says Obama and Karzai met on the sidelines for more than an hour to discuss Afghanistan after 2014, when the bulk of western combat troops are due to depart. They also discussed Afghanistan's upcoming presidential election and the nascent peace negotiations with the Taliban. 

President Karzai said the transition means Afghanistan would no longer be a burden on the rest of the world. 

"I'm bringing to you and to the people of the United States the gratitude of the Afghan people for the support that your taxpayers' money has provided for Afghanistan over the past decade and for the difference it has made to the well-being of the Afghan people," Karzai said. 

The U.S. commitment to Afghanistan will in fact continue until at least 2024. Much of this summit will be spent gathering similar long-term commitments from other countries involved in the Afghan conflict over the past decade; primarily to help build up Afghanistan's security forces. 

According to The New York Times, another shadow hanging over the summit is the continuing tension between the U.S. and Pakistan over an unfinished deal to reopen supply routes for war.
The supply lines were closed in late November after 24 Pakistani soldiers were killed in American air strikes along the border between Afghanistan and Pakistan. 

Meanwhile, protests related to the NATO summit continued Sunday, with thousands marching through downtown Chicago, the Associated Press reports. Subjects of protest ranged from the war in Afghanistan to climate change and the erosion of union rights. Some participants called for the dissolution of the 63-year-old military alliance itself. 

There were even more serious security incidents. Two people were arrested on Sunday, on charges of wanting to blow up the Chicago bridge and set pipe bombs during the summit. On Saturday, three people were arrested for reportedly manufacturing Molotov cocktails with plans to attack targets. 

They face charges of conspiracy to commit terrorism, material support for terrorism and possession of explosives. 

Discussions among NATO officials will continue well into the evening and on Monday, where continued talks about Afghanistan will also include discussion of missile defense and NATO modernization.