BERLIN (Reuters) - Germany has tightened security at Christmas markets across the country a year after a deadly truck attack on a Berlin Christmas market, with conservative Chancellor Angela Merkel under fire from victims’ relatives for her handling of the case.

FILE PHOTO: Flowers and candles are placed at the Christmas market at Breitscheid square in Berlin, Germany, December 30, 2016, following an attack by a truck which ploughed through a crowd at the market. REUTERS/Fabrizio Bensch

Anis Amri, a failed Tunisian asylum seeker with Islamist links, hijacked a truck on Dec. 19, killed the driver and then plowed it into a crowded Berlin Christmas market, killing 11 more people and injuring dozens of others.

About 2,600 Christmas markets reopened in late November with added security staff on patrol and concrete barriers to protect shoppers.

Merkel this week paid a surprise visit to the site of the attack, where a permanent memorial for victims will be unveiled on Tuesday. She will meet on Monday with relatives of victims, many of whom say they felt neglected by the government after the attack.

In an open letter to Merkel published in Der Spiegel magazine this month, victims and survivors complained that the chancellor had not met with them personally.

Kurt Beck, a Social Democratic politician who is representing victims and survivors, told reporters Merkel’s handling of the tragedy stood in contrast with how the French government had responded to terrorist attacks in Paris.

He also blasted what he called an “unbelievable” case in which the family of one victim was sent a bill for an autopsy and then hounded by bill collectors.

“There are incidents which must not be repeated,” Beck said, urging the government to increase hardship compensation for the victims’ relatives and the survivors.

German officials say they have tightened security and increased information sharing among security forces after investigations exposed a range of failures in the Amri case.

But experts say much work remains to be done.

“Cooperation between intelligence agencies and between police authorities must be improved,” said Malte Roschniski, a Berlin security expert.