President Barack Obama maintained a slim lead in several swing states while others were tied in polls released Thursday.

In surveys from Public Policy Polling, Obama led Romney among likely voters in Iowa, 49 percent to 47 percent, a one-point gain for Obama from PPP's survey of Iowa a week ago.

In Wisconsin, likely voters favored the president 51 percent to 45 percent, a four-point gain since PPP's poll there conducted immediately following the first debate.

In Nevada, Obama led Mitt Romney 50 percent to 47 percent, according to a NBC/WSJ/Marist poll released Thursday.

In Colorado, an NBC-Marist College had the rivals tied at 48 percent among likely voters, but a PPP survey gave Obama 51 to 47 percent lead.

Romney was ahead in Virginia, 47 percent to 45 percent among likely voters, according to a new Fox News poll released Thursday. But a new PPP poll had Obama leading 51 to 46 percent there.

In North Carolina, PPP had Obama and Romney tied at 48 percent, a one-point gain for Obama from a previous poll.

National tracking polls released Thursday ranged from 50 to 47 for Romney to 47 to 45 percent for Obama.