Des Moines, Iowa (CNN) Hillary Clinton has a 6 percentage point lead over Bernie Sanders in Iowa, a new poll out just one week before the state's caucuses shows.

The poll is the first since mid-December that meet's CNN's polling standards and shows Clinton with a sizable lead over Sanders. It could signal that momentum is swinging back in Clinton's direction after Sanders surged into the lead in early January.

However, Sanders remains the front runner in New Hampshire, the first primary state, with a 56% to 34% advantage over Clinton, according to a Fox News poll of the Granite State

And Clinton's national lead among likely Democratic primary voters has narrowed -- but is still clear. She's up 49% to Sanders' 37%, a third Fox News poll showed

The Democratic nominating contest has tightened in recent weeks, with Sanders' singular message of addressing income inequality breaking through.

Clinton still holds significant advantages as the contest shifts from Iowa and New Hampshire to Nevada and South Carolina, two states with much larger minority populations -- among whom Clinton leads.

The candidates are set to participate in a town hall at Drake University in Des Moines, Iowa, on Monday night. It is being hosted by Drake and the Iowa Democratic Party and broadcast on CNN at 9 p.m. ET.