MAINZ, Feb 23: At least 4,000 demonstrators vented their anger at the visit of US President George Bush to Germany here on Wednesday but were kept well away from a castle where the president dined.

The centre of the picturesque western city was almost totally deserted after being shut to traffic and pedestrians during Mr Bush's visit. The protesters brandished placards reading "Master of War Go Home" and "Don't Violate Human Rights".

The organizers of the protest, an alliance of pacifist groups under the motto "Not Welcome, Mr Bush", said they were expecting 10,000 people to attend, but police put the numbers at about 4,000. "Everything is very peaceful," said organizers' spokesman Reiner Braun.

The stretch of the Rhine river that flows through Mainz was shut to shipping, but police confirmed that a boat with an anti-Bush protester on board had managed to sail towards a bridge shortly before Bush's motorcade crossed it.

The online version of Focus magazine said that three police launches intercepted the boat before it reached the bridge. Frankfurt, Germany's biggest airport, was closed for 25 minutes on Wednesday morning to allow Bush's presidential jet to land at the nearby US airbase Rhein-Main.

The extent of the security measures for Bush's visit "were hard to understand in our opinion", he added. Jachnow said a total of 4,675 passengers on Lufthansa and other flights were affected by the disruption.

A spokesman for Frankfurt airport confirmed that 104 flights were cancelled because of the US president's arrival but said that bad weather conditions were to blame. There was a 57-kilometre-wide air exclusion zone in operation over Mainz.

Security was also tight in the neighbouring city of Wiesbaden, where Mr Bush visited US troops. A police spokesman said: "The ring road around Wiesbaden is shut off and there are diversions." -AFP