Inviting Rwandan soldiers into eastern Democratic Republic of Congo carries a "high risk of collateral damage", the parliamentary speaker has told the BBC.
Up to 4,000 Rwandan troops have poured over the border since Tuesday for a joint operation with the Congolese army against the Rwandan Hutu FDLR militia.
Vital Kamerhe said the push should be led by forces enjoying popular support.
Meanwhile the DR Congo authorities have reopened roads to aid convoys and UN peacekeeping troops in the area.
The Congolese military shut checkpoints in North Kivu province after Rwandan troops arrived three days ago, triggering fears of a bloody conflict out of sight of the international community.
BBC East Africa correspondent Peter Greste says that given the reputation of all the region's armed groups for gross human rights abuses, concerns are well-founded. There have been no reports of any clashes so far.
The parliament's speaker told the BBC's Network Africa programme: "I must insist on the fact that we cannot today ask the Rwandan army to turn up on Congolese territory, especially in Kivu, without a high risk of collateral damage."
Rwanda has twice invaded DR Congo in recent years and correspondents say many Congolese are likely to distrust their soldiers' presence on Congolese territory.
Congolese President Joseph Kabila has been criticised for not informing parliament about the invitation to Rwandan troops.
DR Congo's ambassador to the UN, Atoki Ileka, said the operation, agreed last month, was necessary to end the violence in the east of the country.
It heralds an unprecedented level of co-operation between neighbours who until now have been openly hostile, our correspondent says.
Rwanda and DR Congo said they were targeting the Hutu rebels of the Democratic Forces for the Liberation of Rwanda (FDLR) in a military push scheduled to last up to two weeks.
Heading for Nkunda?
The leaders of the FDLR, which analysts say is a well-armed and experienced force more than 6,000-strong, have been linked to the 1994 Rwandan genocide.
The FDLR presence on Congolese soil lies at the heart of 15 years of conflict in the region.
Action against the FDLR has been a key demand of the Congolese Tutsi rebel CNDP (National Congress for the Defence of the People), which seized swathes of territory last year but declared a ceasefire last week.
It says the FDLR has been targeting Congolese Tutsis.
CNDP commanders recently announced a split from their leader, General Laurent Nkunda, and have now joined the Rwandan-Congolese force pursuing the FDLR.
AFP news agency reported on Thursday that Congolese and Rwandan troops were heading towards the stronghold of Gen Nkunda in Bunangana, about 30km (20 miles) east of Rutshuru.
On-and-off fighting involving the CNDP, FDLR, the army and pro-government militias has forced more than one million people in North Kivu to flee their homes since late 2006.
Before last month's deal was signed, the UN accused Rwanda and DR Congo of fighting a proxy war in the region - with Rwanda backing Gen Nkunda and DR Congo of working with the FDLR.