French President Francois Hollande declared the series of attacks carried out in Paris on Friday night as constituting an “act of war organised by Islamic State (IS)”.

Hollande declared three days of national mourning after gun and bomb attacks had occurred almost simultaneously at six locations across the French capital on Friday night, claiming the lives of at least 127 people and leaving more than 180 injured.

According to him, the attacks, which were carried out by eight gunmen and suicide bombers, were “organised and planned from outside”, the BBC quotes him as saying.

Following the attacks, Hollande called an emergency meeting of the national security council, raised the security threat level to its highest point and vowed to pursue a “merciless” fight against terrorists.

France has declared a national state of emergency and the country's borders have been closed, with schools, museums and tourist sites in Paris closed after the attacks.

Numerous world leaders have condemned the attacks and expressed solidarity with France including German Chancellor Angela Merkel, Russian President Vladimir Putin, US President Barack Obama, British Prime Minister David Cameron, Turkish President Recep Erdogan, Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas among others.

Bulgaria's top-level officials, including Prime Minister Boyko Borisov, President Rosen Plevneliev and Foreign Minister Daniel Mitov have also expressed their solidarity with France and condemned all kinds of terrorism.

The deadliest attack occurred at the Bataclan concert hall where many people had been held hostages before security forces stormed the building.

The other attacks targeted busy bars and restaurants, with one of the attacks taking place near the Stade de France stadium where a friendly match between France and Germany was held.

All eight of the perpetrators are believed to have been killed, but there were suspicions that accomplices might be on the run.

At present, no group has claimed responsibility for the attacks, but analysts suggest that the perpetrators were most likely affiliates of IS.