Support for an independent Scotland rose in polls before the Sept. 18 referendum as more potential voters picked sides.

The independence camp gained 4 points to 38 percent and its opponents advanced 2 points to 47 percent, according to an ICM poll for Scotland on Sunday. The share of undecided voters fell 7 percentage points to 14 percent. Excluding undecided voters, pro-independence support climbed 2 points to 45 percent and backing for the 307-year-old union with England dropped 2 points to 55 percent.

Scottish First Minister Alex Salmond has said an independent state will walk away from its share of U.K. debt unless it is allowed into a currency union to use the pound, something British Prime Minister David Cameron has ruled out. Salmond wouldn't give an alternative plan in a televised debate earlier this month with Alistair Darling, the leader of the No campaign.

The ICM poll of 1,005 people showed 52 percent said Salmond's currency plan was "unconvincing" and 26 percent said it was convincing, with 22 percent undecided. Forty-two percent said Darling won the debate, 19 percent said Salmond had won, and 39 percent said they did not know.

In a Herald Scotland poll, people intending to vote for Scottish independence rose to 48 percent once undecided votes were excluded, up from 46 percent at the end of July, the newspaper said Sunday, citing a Panelbase poll. Voters for the No camp dropped to 52 percent from 54 percent.

The survey of 1,026 people was conducted Aug. 12-15.