BRUSSELS (Reuters) - Belgium's chief prosecutor named two brothers on Wednesday as Islamic State suicide bombers who killed at least 31 people in the most deadly attacks in Brussels' history but said another key suspect was on the run.
Tuesday's attacks on a city that is home to the European Union and NATO sent shockwaves across Europe and around the world, with authorities racing to review security at airports and on public transport. It also rekindled debate about lagging European security cooperation and flaws in police surveillance.
The attacks came four months after militants, also from IS, carried out bombings and shootings in Paris that killed 129 people. Some Belgian media reports said a forensic link had been established between one of the Brussels bombers, who may have been killed, and the Nov. 13 attacks in the French capital.
Washington announced that Secretary of State John Kerry would visit Belgium on Friday to demonstrate support.
The Belgian federal prosecutor told a news conference that Ibrahim El Bakraoui, 29, one of two men who blew themselves up at Brussels airport on Tuesday, had left a will on a computer dumped in a rubbish bin near the militants' hideout.
In it, he described himself as "always on the run, not knowing what to do anymore, being hunted everywhere, not being safe any longer and that if he hangs around, he risks ending up next to the person in a cell" - a reference to suspected Paris bomber Salah Abdeslam, who was arrested last week.
His brother Khalid El Bakraoui, 27, detonated a bomb an hour later on a crowded rush-hour metro train near the European Commission headquarters, prosecutor Frederic Van Leeuw said.
Both men, born in Belgium, had criminal records for armed robbery but investigators had not linked them to Islamist militants until Abdeslam's arrest, when police began a race against time to track down his suspected accomplices.
That seems to have prompted the bombers to rush into an attack in Belgium after months of lying low, according to the testament found on the laptop.
At least 31 people were killed and 271 wounded in the attacks, the prosecutor said. That toll could increase further because some of the bomb victims at Maelbeek metro station were blown to pieces and victims are hard to identify. Several survivors were still in critical condition.
The Bakraoui brothers were identified by their fingerprints and on security cameras, the prosecutor said. A second suicide bomber at the airport had yet to be identified and a third man, whom he did not name, had left the biggest bomb and ran out of the terminal before the explosions.
Belgian media named that man as Najim Laachraoui, 25, a suspected Islamic State recruiter and bomb-maker whose DNA was found on two explosives belts used in the Paris attacks and at a Brussels safe house used by Abdeslam.
De Standaard newspaper, however, citing an unidentified source, named Laachraoui as the second suicide bomber at the airport.
Khalid El Bakraoui rented under a false name the apartment in the city's Forest borough, where police hunting Abdeslam killed a gunman in a raid last week. He is also believed to have rented a safe house in the southern Belgian city of Charleroi used to mount the Paris attacks.
Turkey said it had detained Ibrahim El Bakraoui near the Syrian border last year and deported him to the Netherlands before he was briefly held in Belgium, then released. "Belgium ignored our warning that this person is a foreign fighter," President Tayyip Erdogan said.
The Brussels attacks came days after a suspected Islamic State suicide bomber blew himself up in Istanbul's most popular shopping district, killing three Israelis and an Iranian.
The Syrian-based Islamist group claimed responsibility for Tuesday's attacks, warning of "black days" for those fighting it in Syria and Iraq. Belgian warplanes have joined the coalition in the Middle East, but Brussels has long been a hub of Islamist militants who operated elsewhere.
A minute's silence was observed across Belgium at noon. Prime Minister Charles Michel cancelled a trip to China and reviewed security measures with his inner cabinet before attending a memorial event at European Commission headquarters with King Philippe, Commission President Jean-Claude Juncker and French Prime Minister Manuel Valls.
"We are determined, admittedly with a strong feeling of pain in our stomachs, but determined to act," Michel told a joint news conference with Valls. "France and Belgium are united in pain more than ever."
Valls played down cross-border sniping over security, saying: "We must turn the page on naivete, a form of carefreeness that our societies have known.
"It is Europe that has been attacked. The response to terrorism must be European."
EU justice and interior ministers will hold an emergency meeting in Brussels on Thursday, the Dutch EU presidency said.
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 radicalised. 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.
Editing by Paul Taylor, Ralph Boulton and Richard Balmforth