BAMAKO (Reuters) - Fifty Malian soldiers died this week during a failed army attempt to seize the Tuareg separatist northern town of Kidal, the West African country's defense minister said on Sunday.

The fresh fighting on Wednesday, the worst since the government and separatist groups signed a preliminary peace agreement last year, threatened to sink struggling peace talks to end a long cycle of Tuareg uprisings.

"In terms of toll, we have recorded 50 deaths unfortunately," Soumeylou Boubeye Maiga said on Malian state television, adding that 40 others were wounded in the failed operation.

Maiga had previously said that 20 soldiers were killed in the combat and 30 were wounded.

The Malian army launched the assault on Kidal after clashes broke out last weekend during a visit to the town by new Prime Minister Moussa Mara.

The Tuareg separatist and the government agreed to a deal brokered by the African Union and the United Nations on Friday to permanently cease fire, exchange prisoners, restart peace talks and accept an international investigation into Wednesday fighting.

(Reporting by Tiemoko Diallo, writing by Bate Felix, editing by G Crosse)