Flights to and from Rīga remained canceled into April 20 as concerns continue about volcanic ash spreading from Iceland to continental Europe, according to a message posted on Latvian carrier airBaltic’s Web site.

“The home base of airBaltic in Rīga, Latvia, remains in restricted airspace and no flights can be operated until further notice,” the message read. “Passengers are requested not to travel to the airports.”

Flights began to be canceled on April 15 as the ash spread from the Eyjafjallajökull volcano in south Iceland. Airspace in Great Britain was the first to be affected, followed by Scandinavia and much of the rest of northern Europe.

Reports early on April 19 suggesting that the volcano was quieting were replaced later by an announcement from Britain’s National Air Traffic Services that the eruption had instead intensified.

“This demonstrates the dynamic and rapidly changing conditions in which we are working,” according to NATS.

Air traffic officials closed the airspace in many countries because of concerns that the volcanic ash could shut down aircraft engines.

Flights were canceled to at least 9 a.m. April 20 Latvian time, airBaltic announced. However, transit flights over Latvia at an altitude from 6-10 kilometers were allowed, a Ministry of Transport spokesperson said.

Almost all flights to and from Estonia’s Tallinn Airport also were canceled. A Lufthansa flight from Munich was still expected to arrive at 9 a.m. local time, according to information posted on the airport’s Web site early April 20. Lufthansa on April 19 renewed most of its long-distance flights, the company announced on its Web site.

Vilnius International Airport announced on its Web site that Lithuanian airspace has reopened, but noted that the decision to fly is up to the pilot of the airplane. Many flights to and from Vilnius remained canceled.