German Chancellor Gerhard Schroeder has officially launched his election campaign - more than three weeks earlier than first planned.

He has been forced to act early by poor opinion polls, which show him trailing his conservative rival, Bavarian governor Edmund Stoiber, by up to seven points.

The Social Democrat chancellor formally launched his bid for a second term in office by addressing a rally of 10,000 people in his home city, Hanover.

The battle for votes is intensifying

"I am utterly convinced that a signal will go out from here: the Social Democrats are getting ready to battle and decide this election with confidence," he told the cheering crowd.

He will later set off in a battle bus on a tour taking in more than 40 towns and cities across Germany.

The prospect of US military action against Iraq appears to be emerging as a key theme in his campaign tactics, although Mr Schroeder has denied trying to exploit the issue for political purposes.

Mr Schroeder has repeatedly questioned the wisdom of military action against Iraq, suggesting that the only way to maintain German opposition to it is to keep the pro-US Mr Stoiber out of power.

"I believe anyone who thinks about intervention must think over the consequences - political and economic," Mr Schroeder told journalists.

Stoiber hopes to attract disillusioned voters

"The world economy is in no state to take new burdens."

But it is Mr Schroeder's economic record which may prove the bigger influence with voters.

Unemployment is now hovering around the four-million mark, and Mr Stoiber has seized on the economy as a campaign weapon - hoping to attract disillusioned voters in Germany's industrial heartlands.

Sleaze allegations have also given Mr Schroeder a continuing electoral headache.

One onlooker was unimpressed by the speech.

"[It] was nothing more than you'd expect before an election. I'm unemployed and I've left the party in the last year. I voted SPD last time, but I won't again. I'm 56 and have been left by the wayside," said Gerhardt Heuer.

Air miles row

Mr Schroeder's speedy sacking of Defence Minister Rudolf Scharping last month has failed to halt further claims of impropriety.

The latest row is over claims that members of the Social Democrat-Green coalition Government misused air miles earned when flying on official business.

Mr Schroeder is hoping to regain the initiative with the rally in his home city of Hanover, but the BBC's Tristana Moore in Berlin says it is widely being seen as a sign of desperation.

Mr Stoiber has had good news on his personal popularity - a field previously dominated by Mr Schroeder.

Although mistrusted by some Germans because of his Bavarian background, Mr Stoiber has achieved an improvement in his personal ratings in the most recent polls.

Opinion polls have consistently given Mr Stoiber a clear lead over Mr Schroeder, with the gap apparently widening as polling day - 22 September - draws closer.