|Thursday's abductions have raised questions about security for foreign mine workers in the region [EPA]
Mauritanian soldiers have clashed with suspected fighters from al-Qaeda's North African wing (AQIM) in Mali, two days after several foreign nationals were abducted in the region.
The fighting began on Saturday on the Mauritania-Mali border but then moved on to Malian territory, Mauritanian security sources said.
The sources told Al Jazeera that at least 12 AQIM members were killed and several more were injured. On the Mauritanian side, five soldiers were killed and five injured.
"We are presently in Malian territory and engaged in full combat," a Mauritanian security source told the AFP news agency.
Hamdi Uld-el Hassen, a freelance journalist in Mauritania's capital, Nouakchott, said the violence is a sign that Mauritania is stepping up its fight against al-Qaeda.
"This was the first palpable challenge to al-Qaeda," he told Al Jazeera.
"Mauritania now is strengthening the military presence along the Malian border and that was a tangible message to al-Qaeda that Mauritania will not stay like it was in the past - waiting to be targeted by al-Qaeda.
"Mauritania now is saying: 'We are following stronger tactics, which [are] breaking al-Qaeda, weakening al-Qaeda, tackling al-Qaeda even on its bases'."
Speculation rose over whether the fighting was related to Thursday's abduction of five French nationals and a Togolese and Madagascan worker from a uranium mining town in Niger.
But a security source in Nouakchott who knew the background to the mission denied this.
"The operation was launched because the opportunity presented itself. It was not planned long in advance," he said.
Security sources in Niger and Algeria said on Friday that the abductors had "crossed the border" between Niger and Mali with the hostages and were in the Malian desert.
Mauritanian troops and French special forces crossed into Mali in July in an attempt to free a French citizen who had been taken by al-Qaeda fighters.
After the captor's execution, France declared it was at war with the group and pledged further military support to countries in the region.
France suspects al-Qaeda's North African wing is also behind Thursday's abductions, but has received no claim of responsibility, Bernard Kouchner, the French foreign minster, said.
Thursday's abductions has raised questions about security for mine workers in the region, where groups linked to AQIM operate.
"We suspect it's the same groups ... linked to the mainstream of AQIM," Kouchner told Europe 1 radio on Friday.
"Unfortunately, we have dealt with them before."
Among the hostages are an employee of the French nuclear group Areva and his wife. In June 2008, four other French workers for Areva were abducted by the Tuaregs and held for four days.
Nicolas Sarkozy, the French president, held emergency security talks with the prime minister, interior minister and armed forces chief on Thursday evening to decide what measures France would take.
The Arlit region of northern Niger, where Areva has its uranium mining operations, was also the location of a simmering Tuareg rebellion, though attacks have died off since fighting eased last year.