Mali, Mauritania, Niger and Algeria will set up, within 18 months, a joint force of up to 75,000 soldiers to secure their shared Sahara-Sahel desert zone, Mali's foreign minister said.

"The number of soldiers in the force tasked with fighting terrorism will increase to 75,000 in the next 18 months," Soumeylou Boubeye Maiga said on Friday.

Leaders from the four nations gathered in Mali to look at security issues, including the fall-out from the conflict in Libya, which experts say has increased the access to arms.

The four nations are struggling to control the zone, where al-Qaeda's North African wing has stepped up attacks and is operating alongside smugglers, rebels and local criminals.

A joint command centre has been established in Tamanrasset, in southern Algeria, but regional rivalries and the lack of trust between the countries have long stymied a coordinated regional approach European nations and the US have called for.

'Threat of terrorism'

"More than ever our people and our countries are exposed to the threat of terrorism, heavy weapons in circulation, drug trafficking and hostage-taking," said Maiga.

Maiga also stressed the need to tackle "trans-national organised crime". He added that it was vital the four countries, which share a military base in  Algeria, acted together against terrorism.

Algeria's delegate, Abdel Kader Messahel, said: "The challenges we face require more focused planning and effective co-ordination. "It falls on us to evaluate dangerous developments and the new dimensions the terrorist threat is taking," he added.

Al-Qaeda in the Islamic Maghreb (AQMI) has several bases in Mali from where it launches operations into the desert region, carrying out attacks, kidnappings of foreigners and drug trafficking.

AQIM is holding four French citizens abducted in northern Niger in September 2010 as well as an Italian kidnapped in southern Algeria in February.