Published: Sep 08, 2011 9:32 AM EDT
Updated: Sep 09, 2011 6:30 AM EDT

HILVERSUM, Netherlands (AP) - Vandals damaged four greens at the Hilversum Golf Club, briefly delaying the start of play at the European Tour's KLM Open on Thursday morning.

Championship director Daan Slooter said parts of the greens at the fourth, fifth, sixth and ninth holes were dug up.

The start of the KLM Open was delayed by 45 minutes Thursday while staff repaired the damage. The motive for the vandalism was not immediately clear.

"I'm very disappointed for all the people here at the club who worked so hard over the past few days, through challenging weather conditions, to ensure the course was in playable condition," Slooter said. The course has been drenched by heavy rain in recent days.

The patched-up grass on the putting surfaces will be treated as ground under repair.

Slooter said security will be "substantially" beefed up following the vandalism.

Top players including Rory McIlroy, Martin Kaymer and Lee Westwood are part of the strongest field ever assembled for the tournament.

Kaymer was among the early starters, while Westwood and McIlroy were teeing off in the early afternoon. Despite the damaged green, some players were beginning their rounds on the ninth hole.