Western Sahara's pro-independence Polisario Front launched an overnight attack on the Guerguerat area on the border between Morocco and Mauritania, the Saharawi press agency SPS said in a statement Sunday.
"The Saharawi army launched four rockets in the direction of... Guerguerat," SPS said, citing a military leader of the separatist Saharawi forces.
Morocco launched a military operation on November 13 in the buffer zone of Guerguerat, in the extreme south of the former Spanish colony, to drive out a group of Saharawi militants who were blocking a transit route to neighbouring Mauritania.
The statement also reported attacks along the security wall that separates Saharawi fighters from Moroccan forces in the vast desert territory.
A senior Moroccan official contacted by AFP in Rabat said: "There was harassing fire near the area of Guerguerat, but it did not affect the trunk road, traffic was not disrupted."
Western Sahara is a disputed and divided former Spanish colony, mostly under Morocco's control, where tensions with the Polisario Front have simmered since the 1970s.
In November, Morocco sent troops into a UN-patrolled buffer zone to reopen a key road leading to Mauritania.
The Polisario responded by declaring a 1991 ceasefire null and void, arguing the road had not existed when the truce was signed.
The two sides are reported to have since exchanged regular fire along the demarcation line.
UN-led negotiations involving Morocco and the Polisario, with Algeria and Mauritania as observers, have been suspended since March 2019.
The Polisario Front fought a war for independence from Morocco from 1975 to 1991.
The UN-backed ceasefire deal was meant to lead to a referendum on self-determination.
Morocco has offered autonomy, but maintains the territory is a sovereign part of the kingdom.
Under former president Donald Trump, Washington last year broke decades of precedent by recognising Morocco's full sovereignty over the territory, in exchange for Rabat normalising relations with Israel.