Niger's army has clashed with a heavily armed convoy of vehicles that entered its territory from Libya, killing 13 in the convoy and suffering one casualty on its side, military sources in the West African country said on Wednesday.

The sources said Nigerien authorities took a further 13 prisoners after the incident, which took place on Sunday around the remote northern Nigerien mining town of Arlit just south of the border with Libya.

I understand it was a convoy of pro-Gaddafi Libyans guided by Malian Tuaregs, said one army officer who declined to be named, adding that some members of the convoy had fled.

Niger's government said late on Tuesday there had been a clash, without specifying that the convoy had come from Libya, where forces loyal to slain leader Muammar Gaddafi have been routed by NATO-backed rebels now in control of the country.

The government statement said Nigerien forces had seized arms including 36 assault rifles, 11 machine guns, three rockets and over 11,000 cartridges of different calibres.

Hundreds of thousands have fled Libya south into Niger and neighbouring Mali in past months. The vast majority are migrant African workers who had settled in Libya, but authorities have also signalled the return of some armed pro-Gaddafi fighters.

Niger has taken in Gaddafi loyalists including four generals and his son Saadi, saying it is sheltering them on humanitarian grounds. Niger has not commented on speculation that another Gaddafi son, Saif al-Islam Gaddafi, has sought to enter Niger.

However it has said that if he did, it would fulfill its commitments to the Hague-based International Criminal Court, which has issued an arrest warrant for him over alleged crimes against humanity.

Governments in the Sahel are worried that Libyan arms depots used by Gaddafi have been raided and that the weapons may be falling into the hands of rebel groups and local al-Qaeda allies responsible for kidnappings and attacks on government sites.

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