In an interview with Russian media, Assad accused Europe of supporting "terrorism" and providing "protection for terrorists, calling them moderates."
"How can one be indignant about a drowned child and remain silent about the deaths of thousands of children, elderly people, women and men killed by terrorists in Syria?" Assad said.
Hungary's foreign minister denied that closed borders and tough new laws signal callousness toward refugees, repeating the government's claim that most of those entering Hungary are actually economic migrants.
"Based on our history, we are always in solidarity with the refugees," Peter Szijjarto told The Associated Press in an interview. "What we're saying is that we cannot accept economic migrants because we cannot bear the burden of that."
Most of the migrants who had hoped to cross into Hungary were still trapped along the border in Horgos, Serbia, however. Many were confused about whether to keep waiting or to try to enter the EU through Croatia, a longer and less direct path into Western Europe.
Melita Sunjic, a spokeswoman for the UN refugee agency, said that early in the day the migrants were refusing to leave the border but changed their minds because of news and rumors going around that Croatia's borders were open.
Most hope to reach Germany, where Chancellor Angela Merkel's government has said it expects some 800,000 refugees to arrive in Germany this year alone. The vice chancellor has said the number could even reach 1 million.
"I don't know what to do - stay here or try some other way to cross the border," said Ahmed Sami from Aleppo, Syria. "We walked and traveled for hundreds, thousands of kilometers only to be stopped meters from the European Union. My wife and children cannot stand on their feet any more. This is tragic."
At least two buses with about 100 people were seen leaving for the Croatian border from Kanjiza, a Serbian town on the border with Hungary.
About 300 crossed into Tovarnik, Croatia, after they were bused to the Serbian border town of Sid on an all-night ride from Macedonia.
Croatian Prime Minister Zoran Milanovic criticized Hungary's decision to seal its border with Serbia for migrants and said Croatia will not do the same.
"We are ready to accept these people, regardless of their religion and the color of their skin, and direct them to the destinations where they wish to go, Germany and Scandinavia," Milanovic told lawmakers in Parliament.
"Barbed wire in Europe in the 21st century is not an answer, it's a threat," Milanovic said.
Migrants have avoided Croatia in the past because they must still go into Hungary or Slovenia before reaching Austria or Germany.
Elsewhere in Europe migrants remained on the move.
Greek police said about 5,000 refugees and migrants crossed the country's northern border with Macedonia in the 24 hours from Tuesday morning to Wednesday morning.
Meanwhile, Austria began selective controls of vehicles at three main border crossings with Hungary as it tries to impose some order over the stream of people.