BERLIN (AP) — A German aid group says its volunteers were attacked after helping prepare a new refugee shelter near the eastern state of Saxony.

The Federal Agency for Technical Relief, or THW, says bottles were thrown late Friday and attempts were made to prevent staff from leaving the site in Niederau. Manuel Almanzor, a THW official, said Saturday he was "deeply shocked" by the attack against volunteers carrying out humanitarian work.

Police in Dresden say 20 drunken youths tried to pull down a fence around the site and threw bottles and cigarettes at THW staff.

Steffen Kuehnel of the Dresden police said criminal complaints would be filed against those responsible, but nobody had been arrested.

German officials have counted over 400 attacks against refugees and shelters this year.