Washington - The chief champaign strategist of Democratic Party presidential candidate Hillary Clinton has resigned, according to US media reports on Monday.

There was no information from the Clinton camp as to the reason behind the late Sunday withdrawal of Mark Penn from the Clinton campaign, which is running second in the country's Democratic party primaries to nominate a candidate for president.

United States media has speculated that the resignation was due to Penn's activities as a lobbyist in favour of a trade treaty with South American country Colombia.

Penn in his capacity as a paid lobbyist was reported to have met with the Colombian ambassador to the United States last week. Clinton, wife of former US president Bill Clinton, opposes a treaty with Colombia due to its allegedly deleterious effect on US labour.

Clinton's former campaign manager Patti Solis Doyle as well as Doyle's deputy Mike Henry resigned just in February in connection to Clinton's unexpectedly weak performance in the February 5 "Super Tuesday" primary elections in various US states.

Clinton, a US senator for the state of New York, is currently running second behind Barack Obama. (dpa)