The race for the White House heats up this week with the Democratic party contenders for the presidential nomination facing off in two key primary elections on Tuesday, in Indiana and North Carolina.

Barack Obama and Hillary Clinton are practically neck and neck in Indiana, while Obama, an Illinois senator, is leading in North Carolina, which has a large African-American population. At stake Tuesday are 187 Democratic delegates.

Democratic presidential hopeful Senator Hillary Rodham Clinton signs autographs during a campaign rally at Indiana University in Bloomington, Ind., on Friday. (Elise Amendola/Associated Press)Obama has an overall lead among delegates for the Democratic convention in August, but Clinton's recent victory in Pennsylvania has given her campaign a new lease on life.

Both candidates traded barbs on foreign policy issues Sunday, with Obama taking Clinton to task for threatening to "obliterate" Iran if that country uses nuclear weapons to attack Israel.

Obama said his opponent reminded him of President George W. Bush with her bellicose rhetoric.

Speaking at a party event in Indianapolis, Clinton said she wanted to send a message to Tehran that her presidency would be a staunch ally to the Jewish state, and the costs of nuclear aggression were high.

In the final hours before Tuesday's primaries, both candidates had punishing schedules. Clinton was holding five events across the two states, while Obama was flying from Indiana to North Carolina and back again over several hours. Both began their day at dawn and are expected to end it well into the night.

While the U.S. national media have focused on the Iran exchange between the candidates, the CBC's Jennifer Westaway reported that local issues are at the fore in Indiana — a Midwestern state with both a farming and industrial economy and concerns about job losses and globalization.

Westaway said Clinton is sounding as if she were a "Hoosier" — the local nickname for people from Indiana.

Gas tax holiday a 'shell game,' says Obama

Clinton, a New York senator, is also playing up her proposal to give U.S. drivers a break on gas taxes this summer, which her opponent says would save consumers about 30 cents a day at most and which many economists oppose.

"Does anyone here really trust the oil companies to give you the savings, instead of pocketing the money themselves?" Obama asked an election rally crowd in Indianapolis. "It's a shell game."

Obama used to have a clear lead over Clinton in Indiana, a neighbouring state to his own Illinois, but she has gained on him in recent weeks.

So far, Obama has 1,743.5 pledged delegates and superdelegates, compared to Clinton's 1,607.5, according to an Associated Press count Monday. Eight pledged delegates, each with half votes, attended the Democratic presidential caucuses in the U.S. island territory of Guam over the weekend.

Analysts say even a big Clinton victory in Indiana wouldn't challenge Obama's edge among committed delegates to the Democratic convention, but the psychological effect on what are known as superdelegates, party officials and members of Congress who vote as they please in the nomination process, would be considerable.

Both candidates predicted the race would stretch into June, regardless of Tuesday's outcomes.

With files from the Associated Press