The head of Germany’s public health agency, the Robert Koch Institute (RKI), said Monday that he was concerned by a “disturbing” rise in COVID-19 cases over the past week.

“The new developments in Germany make me very worried,” RKI head Lothar Wieler told reporters. “The rise has to do with the fact that we have become negligent.”

Germany has registered a daily average of 557 new cases over the past seven days. There were 633 new infections on Tuesday, a jump from 340 new cases the previous day.

Wieler urged citizens to remember social distancing measures and reiterated the importance of wearing a mask in public.

Chancellor Angela Merkel’s chief of staff, Helge Braun, also called the rise in cases a "cause for concern." She said cases need to be kept under 500 new infections a day during the summer, in order for the country to handle a second wave of the virus in the fall.

Germany’s response to the COVID-19 pandemic has often been praised as effective, due to the country’s wide-spread testing regime and its oversupply of hospital beds. There have been some outbreaks at German meatpacking plants in recent months, forcing some communities to shut down businesses and other public spaces.

Germany closed down schools, shops, restaurants, playgrounds and other spaces nationwide in March to halt the spread of the virus. The country began to reopen on April 20, but Germans are required to wear masks in stores and on public transit.

In order to keep cases from rising, Germany has asked vacationers to not travel to the Spanish region of Catalonia. The region has been seeing daily increases of more than 1,000 new cases, forcing the Spanish government to implement new lockdown restrictions. 

As of 4:30 p.m. ET on Tuesday, there are 207,474 COVID-19 cases and 9,128 deaths in Germany, according to data from Johns Hopkins University.