Belgian police have arrested 16 people in a major anti-terror operation, but on-the-run Paris attacker Salah Abdeslam remains at large, a federal prosecutor has said.
No arms or explosives were found in 19 raids across Brussels - including the Molenbeek area from where the Paris attack was planned - or two in Charleroi, they said.
Abdeslam was said by Le Soir newspaper to have been identified fleeing in the direction of Germany in a BMW.
The authorities urged a social media blackout of operations as the desperate manhunt continued for surviving members of the group behind the gun and bomb murders of 130 people in the French capital.
Brussels remained on high alert over fears of a Paris-style Islamic State (IS) terror attack as David Cameron prepared to meet Francois Hollande to discuss action to crush the extremist threat.
Schools, universities and the underground system will remain closed today and some workers have been advised to stay at home while key suspects remain at large.
As the search for the jihadists went on, world leaders were contemplating how to respond to a string of outrages - also including the downing of a Russian airline over Egypt - with the UK moving nearer to joining allied air strikes in Syria.
Prime Minister Mr Cameron will present the case for escalating British military involvement to Parliament later this week - with the Paris attacks and an unanimous United Nations Security Council resolution apparently galvanising support among MPs.
He is meeting Mr Hollande in Paris as the French president starts an intensive push to create a "grand coalition" to destroy IS - also known as Isil, Isis and Daesh - which will take him to Washington and Moscow in the coming days.
A Commons vote on air strikes could be held as early as next week and Chancellor George Osborne said the deaths of 130 on the streets of Paris and the UN resolution backing "all necessary measures" were swaying the argument.
"We'll make the case as a government, we will allow MPs to digest that response and then we will see where we stand.
"Frankly, Britain has never been a country that stands on the sidelines and relies on others to defend us," he said.
Mr Cameron's case will come in the form of a response to a report by the Commons foreign affairs committee which expressed severe reservations about the coherence of the Government's case.
Its Conservative chairman Crispin Blunt has indicated the conditions set in the report could now be met.
Labour leader Jeremy Corbyn has said the UN vote should be a catalyst for renewed efforts to find a political solution in Syria, not "external intervention", but dozens of his MPs are ready to back strikes.
It appears increasingly likely they will be granted a free vote to avoid forcing possible frontbench resignations over the issue.
The Democratic Unionist Party has signalled it is willing to back air strikes but the Scottish National Party - the third-biggest in the Commons with 55 MPs - says it could not without a commitment to seek explicit UN authorisation for military action.
Some of the Tory MPs who joined a 2013 rebellion against air strikes - helping inflict the defeat on Mr Cameron that has caused a wariness to commit to intervention - indicated that they were likely to change sides.
With Brussels on the highest Level 4 alert, officials recommended the cancellation of sports competitions and the closure of shopping centres and public buildings.
The Great Britain tennis team delayed its departure for next week's Davis Cup final, due to be played at the 13,000-seat Flanders Expo in Ghent, which is only 35 miles north east of Brussels.
More than 1,000 British fans are expected to support the team but the Foreign Office is advising visitors to Belgium against places with large numbers of people.
In Paris, French police issued a photo of the as-yet-unidentified third attacker who died outside the Stade de France stadium.
The BBC said the picture issued by French police matched that on paperwork relating to a man who entered Greece posing as a Syrian refugee along with another of the terrorists.
He was travelling on a passport in the name of "M al-Mahmod" although his actual identity remains unclear.
A Syrian passport in the name Ahmad al-Mohammad was found with the remains of another of the group - who is recorded as arriving on the Greek island of Leros from Turkey on a boat with nearly 200 refugees.
The pair appear to have made the journey to Paris together.