Armed soldiers on a Brussels street. (AAP)  The Belgian capital is locked down for a second day with police and troops on the streets as the authorities hunt for several suspects linked to the Paris attacks.  With the world on edge over the jihadist threat, US President Barack Obama said the most powerful tool to fight the terror of the Islamic State extremist group was to say "that we are not afraid".  In Paris, Defence Minister Jean-Yves Le Drian said a chemical or biological attack "was among the risks" but that all possible precautions had been taken.  Belgian officials were due to meet later on Sunday to decide whether to extend the security alert in Brussels, imposed over fears jihadists were plotting similar strikes to the attacks in Paris which left 130 people dead on November 13.  The city's metro system and public buildings were closed on Saturday, with shops and restaurants following suit after the terror alert was raised to the highest level of four because of what officials said was an "imminent threat."  Interior Minister Jan Jambon said the authorities were looking not just for Paris suspect Salah Abdeslam, who managed to slip past French security forces after the carnage in the City of Light.  He warned that the capture of Abdeslam, a Belgian-born 26-year-old whose brother blew himself up at a cafe in Paris, would not in itself end the threat.  The UN Security Council on Friday authorised nations to "take all necessary measures" to fight IS jihadists after a wave of attacks, including the downing of a Russian aircraft in Egypt with the loss of 224 lives and the storming of a luxury hotel in Mali which left 19 dead.  Obama said Sunday he would press ahead with a visit to Paris for UN climate talks in December, calling on world leaders to show similar resolve.  Russian President Vladimir Putin said the Mali attack, in which six Russians died, "confirms that terrorism knows no borders and is a real danger for the whole world".  In Turkey, police arrested a Belgian of Moroccan origin in the resort of Antalya, the site of last week's G20 summit, along with two other suspects, probably Syrians.  Ahmet Dahmani, 26, reportedly scouted out targets for the Paris attacks.  The suspected ringleader, Abdelhamid Abaaoud, was killed in a massive police raid on Wednesday along with his cousin Hasna Aitboulahcen, reportedly a one-time party girl who turned to radical Islam about six months ago.  Police also found the body of an unidentified suicide bomber, who, according to DNA tests, is not known to police.  In all, seven attackers died in Paris.  The European Union agreed Friday to rush through reforms to the passport-free Schengen zone.
Brussels has closed its metro system and shops and cancelled concerts as the prime minister said authorities feared a "Paris-style" series of attacks.