BERLIN — Ukraine’s president, Volodymyr Zelensky, has accused Germany of putting its economy before his country’s security in the run-up to the Russian invasion.

In an address to Germany’s parliament Thursday, Mr. Zelensky criticized the German government’s support for the Nord Stream 2 pipeline project meant to bring natural gas from Russia. Ukraine and others had opposed the project, warning that it endangered Ukrainian and European security.

Mr. Zelensky also noted Germany’s hesitation when it came to imposing some of the toughest sanctions on Russia for fear it could hurt the German economy.

The Ukrainian president called on Germany not to let a new wall divide Europe, urging support for his country’s membership of NATO and the European Union.

Meanwhile, as Russia’s invasion of Ukraine entered its fourth week on Thursday, Russian forces were largely bogged down outside major cities and shelling them from a distance, raining havoc on civilians.

In the besieged southern city of Mariupol, a Russian airstrike destroyed a theater where hundreds of people were sheltering, burying many of them in the rubble, Ukrainian officials said. They said the number of casualties in the Wednesday attack was unclear as the entrance was blocked by debris.

The strike came as Mr. Zelensky invoked 9/11 during an urgent appeal to Congress for more weapons to stem the Russian assault. President Biden announced an additional $800 million for Ukraine’s military and said President Vladimir Putin is a “war criminal.”

Mr. Putin meanwhile warned against attempts by the West and his Russian opponents to bring about the “destruction of Russia,” signaling an even greater crackdown on opposition to the war.

He said Russians “will always be able to distinguish true patriots from scum and traitors and will simply spit them out like a gnat that accidentally flew into their mouths.”

The fighting has led more than 3 million people to flee Ukraine, the U.N. estimates. The death toll remains unknown, though Ukraine has said thousands of civilians have died.

In peace talks, Mr. Zelensky’s adviser Mikhailo Podolyak said Ukraine is demanding a cease-fire, the withdrawal of Russian troops and legal security guarantees for Ukraine from a number of countries. Ukrainian and Russian delegations held talks again Wednesday by video.

Another official in Mr. Zelensky’s office, speaking on condition of anonymity because of the sensitivity of the talks, said the main subject under discussion was whether Russian troops would remain in separatist regions in eastern Ukraine after the war and where the borders would be.

Just before the war, Russia recognized the independence of two regions controlled by Russian-backed separatists since 2014 and extended the borders of those regions to areas Ukraine had continued to hold, including Mariupol.