The Rwandan-backed M23 rebels have attacked Congolese government forces in the South Kivu province, breaking a two-day lull in fighting.

Heavy shelling began on Tuesday morning, three days after a summit of East and Southern African leaders called for an immediate and unconditional ceasefire.

The rebels have seized vast swathes of land in the eastern DR Congo, including the major city of Goma.

They are now pushing towards Bukavu, the capital of South Kivu - another key city in the region.

Around 2,900 people have been killed since early January as a result of the hostilities, the latest UN figures suggest.

Approximately 700,000 others are estimated to have been forced from their homes and thousands more injured.

Tuesday's fighting erupted near Ihusi, a locality around 70km (43 miles) from Bukavu and 40km from the South Kivu's airport, security sources told news agency AFP.

A spokesperson for the Congo River Alliance (known by its French acronym AFC), an alliance of rebel groups including the M23, suggested its fighters could take their battle to Bukavu.

Lawrence Kanyuka responded to the arrests by the Congolese authorities of 84 army personnel for crimes such as killing civilians near Bukavu, saying: "If these crimes persist, we will take full responsibility to eradicate the threat at its source and protect our people".

Meanwhile, reports say that hundreds and thousands of refugees, who have fled the ongoing fighting, were being forced to return home by the M23.

The M23 has denied this allegation, but French broadcaster RFI reported that several large camps for displaced people have been dismantled and their inhabitants made to trek back to their villages in conflict zones.

Ocha, the UN's humanitarian agency, said the M23 had given displaced people in Goma 72 hours to return to home.

Mr Kanyuka said such reports were "propaganda" and that displaced people were returning voluntarily. The M23 "does not compel anyone to return without firm security guarantees", he said.

The M23, which is made up of ethnic Tutsis, say they are fighting for minority rights, while DR Congo's government says the rebels are seeking control of the eastern region's vast mineral wealth.

DR Congo and the UN accused Rwanda's Tutsi-dominated government of backing the M23 - an allegation which Kigali has persistently denied.

But recently, the official response has shifted, with government spokespeople stating that fighting near its border is a security threat.