Both Democratic party White House hopefuls in the United States claimed gains from Tuesday's split decision in primary elections in North Carolina and Indiana, but Barack Obama's lead is growing as Hillary Clinton's campaign deals with mounting money problems.

Senator Hillary Clinton narrowly won Indiana in the latest U.S. primaries, but Barack Obama's clear victory in North Carolina gives him the edge in the race for the U.S. Democratic party presidential nomination. (Elise Amendola/Associated Press)In another development, George McGovern, an early Clinton supporter, delivered another blow to the New York senator's campaign on Wednesday by throwing his support behind Obama and urging Clinton to drop out of the race.

The former senator and 1972 Democratic presidential candidate said it was virtually impossible for Clinton to win the nomination after Tuesday's results.

"She has run a valiant campaign, and she will remain an influential voice in the American future," he said.

Speaking to reporters in West Virginia on Wednesday, Clinton vowed to stay in the race "until there is a nominee," while adding she still believes she is the best choice for Democrats to campaign against Republican nominee John McCain.

"I believe I'm the stronger candidate against Senator McCain and I believe I would be the best president among the three of us running," Clinton said. "So we will continue to contest these elections and move forward."

Obama leads popular vote

In the latest voting tallies, Obama won easily in North Carolina, while Clinton eked out a narrow victory in Indiana.

With six contests left, Obama leads in the popular vote and was 178.5 delegates shy of the 2,025 that the national Democratic party says he needs to secure the Democratic nomination.

In one of his trademark rousing speeches, Obama told wildly cheering supporters in Raleigh, N.C., that he was the clear winner of the evening.

"Tonight we stand less than 200 delegates away from securing the Democratic nomination for president of the United States," he told the crowd, which answered with chants of "yes we can, yes we can."

CBC's Neil Macdonald, who was at the rally, said Obama not only took an overwhelmingly high percentage of the black vote in North Carolina, but also "a good share" of the white vote, despite Clinton's "strenuous efforts to deny him that."

"She had gone very populist here, posing as a beer-drinking, gun-loving, tax-cutting populist," Macdonald said. "She mocked Obama as an elitist. It didn't work."

Obama won a comfortable 56 per cent of the vote in North Carolina, to Clinton's 42 per cent, a triumph that mirrored earlier victories in southern states with large black populations.

Another factor in his favour, analysts said, was the presence of affluent white and Asian voters in the prosperous, high-technology area around Raleigh. Such people have been Obama supporters in other states.

Florida, Michigan matter: Clinton

In Indiana, it was after midnight local time when Clinton emerged with a narrow victory, winning just over 51 per cent of the vote.

She told her supporters at campaign headquarters in Indianapolis that she wasn't giving up, despite Obama's now considerable lead in committed delegates to the party convention in August where the presidential nominee will be chosen.

Democratic presidential hopeful Barack Obama and his wife Michelle greet supporters at a primary election night rally in Raleigh, N.C., on Tuesday. (Jae C. Hong/Associated Press)"Thanks to you, it's full speed on to the White House," Clinton said, signalling her determination to fight on in a campaign already waged across more than 16 months and nearly all 50 U.S. states.

Though she has no statistical chance of winning the nomination from the remaining primary state elections, Clinton is again pressing for two states where primary results favourable to her were disallowed — Florida and Michigan — to hold new votes, giving her a boost into the August convention.

"It would be a little strange to have a nominee chosen by [just] 48 states," she said in Indianapolis.

Observers say Obama's campaign and the Democratic party leadership have already rejected that idea and there are fears of a protracted and politically damaging legal battle if Clinton continues to insist on including Florida and Michigan to up her delegate totals.

After the latest two primaries, Obama won at least 94 delegates, and Clinton 75, with 18 still to be awarded. That gives Obama an unassailable lead among elected delegates, with the votes of so-called super-delegates — elected officials and Democratic party office bearers — increasingly crucial. Clinton's lead among this group is narrowing rapidly as more and more of them opt for Obama, making their choice based on his big lead in the popular vote.

CBC's Henry Champ in Indianapolis said things are looking dark for the Clinton campaign.

"There's another issue that's bedevilling her," Champ said, "and that's money. The latest developments don't augur very well. A lot of people who have been contributing to her campaign will now be wondering if it's not time to close their chequebooks."

The Associated Press reported that Clinton lent her own campaign $6.4 million US over the past month, more than doubling her investment in her own election bid.

Obama has routinely outspent Clinton throughout the primaries, and his campaign budget is still receiving donations from a vast network of mostly small- and medium-sized donors. In the latest primaries, he spent nearly twice what Clinton did on television advertisements, seen as key to swaying undecided voters.

Exit polls in both Indiana and North Carolina showed the economy was the most important issue to voters, followed by the Iraq war.

Concerns about Obama's controversial former pastor, Jeremiah Wright, and Clinton's attempts to paint him as an out-of-touch elitist did not seem to be important to many voters.

With files from the Associated Press