|Thursday's blast ripped the facade off the Argana cafe in Marrakesh's iconic Jamaa el-Fna square [EPA]
Moroccan authorities have stepped up security following Thursday's bomb blast at a cafe in Marrakesh in which at least 16 people were killed, including 11 foreigners.
A senior police official said cordons have been erected at the entrances to Morocco's main cities and security forces deployed across the country, "to ensure the internal security of the country".
"Preliminary investigation ... suggests that this was a terrorist act caused by an explosive device," the official MAP news agency quoted Taieb Cherkaoui, the interior minister, as saying on Friday.
Khalid Naciri, a government spokesman, told the Associated Press news agency it was too soon to say who had carried out what he called a terrorist attack.
Interpol, the international police agency, condemned the attack and said it would ensure "the Moroccan authorities investigating this terrible attack have the full support of the global law enforcement community."
French intelligence and anti-terrorism experts will travel to Marrakesh on Friday to help in the probe, a source said.
Police sought to restore calm in the iconic Jamaa el-Fna square, a cultural heritage site frequented by tourists, while investigators worked to determine how it was carried out and who was responsible.
Police were at the site searching for clues on Friday morning, keeping back onlookers who showed up to see the dramatic sight. The explosion ripped off the facade of the Argana cafe, leaving awnings dangling.
Hillary Clinton, the US secretary of state, condemned the "cowardly attack" and pledged support for Morocco, which is considered a US ally in the region.
France condemned the blast as being "cruel and cowardly" and confirmed there were French casualties.
Nicolas Sarkozy, the French president, learnt "with consternation of the terrorist attack," his office said in a statement.
"He condemns with the greatest firmness this odious, cruel and cowardly act that has caused many casualties, including French citizens," it said.
The United Nations, Britain, Germany, Spain and the Council of Europe human rights watchdog also condemned the attack.
William Hague, the British foreign secretary, described it as "utterly reprehensible, and said alleged links to terrorism were worrying.
Al-Qaeda's affiliate in North Africa stages regular attacks and kidnappings in neighbouring Algeria.
Morocco, however, has been mostly peaceful since it was hit by five simultaneous terrorist bombings in Casablanca in 2003 that killed 45 people and a dozen bombers believed linked to the Moroccan Islamic Combatant Group.