EU justice and interior ministers will hold an emergency meeting in Brussels on Thursday, the Dutch EU presidency said.
Valls urged the European Parliament to pass immediately a law allowing the sharing of airline passenger name records (PNR), long blocked by the left. But his own French Socialists said the bill was in the works and French and European political leaders should stop making scapegoats.
"The truth is that PNR would not have stopped either the Paris attacks or the Brussels ones," the French Socialist group in the European legislature said in a statement.
More than 1,000 people gathered around an improvised shrine with candles and street paintings outside the Brussels bourse.
Belgium's crisis coordination centre kept the level of security alert at the maximum as the man hunt continued. Some buses and trains were running but the metro and the airport were closed, along with key road tunnels in Brussels.
The blasts fuelled political debate across the globe about how to combat militants.
Donald Trump, the front-runner for the Republican nomination to succeed Obama in November's U.S. election, suggested suspects could be tortured to avert such attacks. He also said in a British television interview that Muslims were not doing enough to prevent that kind of violence.
After a tip-off from a taxi driver who unwittingly drove the bombers to the airport, police searched an apartment in the Brussels borough of Schaerbeek late into the night, finding another bomb, an Islamic State flag, 15 kg of the same kind of explosives used in the Paris attacks and bomb-making chemicals.
An unused explosive device was also found at the airport.
Security experts believed the blasts were probably in preparation before Friday's arrest of locally based French national Abdeslam, 26, whom prosecutors accuse of a key role in the Nov. 13 Paris attacks.
He was caught and has been speaking to investigators after a shootout at an apartment in the south of the city, after which another Islamic State flag and explosives were found.
About 300 Belgians are estimated to have fought with Islamists in Syria, making the country of 11 million the leading European exporter of foreign fighters and a focus of concern in France and other neighbours over its security capabilities.
Reviving arguments over Belgian security policies following the Paris attacks, in which 130 people died in an operation apparently organised from Brussels, French Finance Minister Michel Sapin spoke of "naiveté" on the part of "certain leaders" in holding back from security crackdowns on Muslim communities.
Belgian Foreign Minister Didier Reynders retorted that each country should look to its own social problems, saying France too had rough high-rise suburbs in which militants had become radicalized. Valls said France had no place teaching Belgium lessons and had problems with its own communities.
Brussels airport seemed likely to remain shut for several days over the busy Easter holiday weekend, since the departure hall was still being combed as a crime scene on Wednesday and repairs can only begin once investigators are finished.