Both Republican front runners in the race to be president are accusing the other of dirty tricks in advertising campaigns.

They each say the other has broken a promise not to use negative campaigning in their respective television adverts.

Now both John McCain and George W Bush are set to use commercials to accuse the other of breaking the deal.

A new campaign by Vietnam veteran John McCain shows the two rivals shaking hands with the accompanying voiceover: "This is George Bush shaking hands with John McCain, promising not to run a negative campaign."

The next image is from a new George W Bush advert but with the McCain commentary: "This is George Bush's new negative ad attacking John McCain and distorting his position."

Mr Bush, the Texas governor and favourite for the Republican nomination, is also planning a new advert this week.

It will feature a Republican debate in Michigan, and then viewers will be remind "that John McCain made a promise not to run negative ads and then he has run them."

Mr Bush is also contemplating commercials attacking areas of Mr McCain's past record.

In campaign exchanges both candidates are also trying to pitch themselves as the Republican's reformer.

Mr Bush said that he, not Mr McCain, was the Republican's "reformer with results", changing both the style and substance of his campaign.

He told supporters: "If you're tired of no results and simple, empty rhetoric, if you're tired of people saying one thing and doing another, come and join my team."

Mr McCain hit back: "I guess Governor Bush is now a reformer. If so, it's his first day on the job."

Delaware in the shadows

The negative campaign row between the party's two big hitters has overshadowed Tuesday's Delaware primary.

Mr McCain is not standing in the state - he says he strategy is dependent on winning South Carolina on 19 February.

And Mr Bush, who is standing in the state, is scrambling to regain his footing after Mr McCain's win in New Hampshire.

For Steve Forbes, the Republican outsider in the race, Delaware could be the end of his participation.

Analysts say a poor showing in the state will force millionaire Mr Forbes out of the race and some fear he will even end up with fewer votes than Mr McCain, who even though he is not officially competing is still on the ballot paper.

Democratic candidates Al Gore and Bill Bradley have been competing for the party's core constituencies - minorities, women and union members.

Gearing up for the coast-to-coast primaries on 7 March, Mr Bradley campaigned for black support in Florida, while the vice president steered his drive for union and gay support to a construction site in New York