Democratic presidential frontrunner Barack Obama has expanded his thin lead over rival Hillary Clinton, garnering seven delegates in Iowa as the close and acrimonious contest marred by a string of race rows chugged ahead claiming more victims.

Half the 14 delegates allocated to John Edwards, who dropped out of the contest in January, switched on Saturday and Obama got most if not all of them, US media reports said.

Democratic Party officials in Iowa said that with more than 86 per cent of the delegates picked, Obama claimed 52 per cent of the delegates elected at county conventions, compared to 32 per cent for Clinton.

Democratic Party projections said the results mean Obama increased by seven the number of delegates he bagged from the state, upping his tally to 23. Clinton got 14, Edwards seven delegates with one to be decided.

After incorporating Iowa's results, the delegate tally showed Obama leading with 1,610 delegates while Clinton had 1,496. A total of 2025 delegates are required to win the nomination at the party convention in Denver in August.

Obama won the state's precinct caucuses in January with 39 per cent of the vote, with Edwards narrowly edging Clinton to finish second.

''Every single one counts and that's why we've been here organising,'' said Teresa Vilmain of Clinton campaign.

Controversies continue to mar the campaigns. What should have been a good week for Barack Obama has turned into one of the worst of his campaign.

Despite winning the Mississippi primary and increasing his lead in convention delegates, he was thrown off stride by dealings with a former fundraiser and inflammatory remarks by his one-time pastor, the Rev. Jeremiah Wright.