Chad has offered to send troops to the Central African Republic to help fight rebels it claims are backed by Sudan.
Since a rebellion began in Sudan's Darfur region nearly four years ago, violence has spilled over its borders into eastern Chad and northern CAR.
Prime Minister Pascal Yoadimnadji said as Sudan was attempting to destabilise both Chad and CAR there should be a "general mobilisation" of the people.
During a three-week long offensive, CAR rebels have captured three towns.
Earlier this week, an UN official said up to 10,000 people had fled the latest rebel advance in the north-east.
At the same time, the Chadian government has declared a state of emergency in the south-east, where escalating violence has forced some 70,000 villagers from their homes.
During a speech to the National Assembly the prime minister said that Chad could not remain indifferent to the plight in CAR.
"A popular saying goes that if your neighbour's house is on fire, you go to help him, or you risk the fire spreading to your house," Mr Yoadimnadji said.
"At the moment we speak, two columns of mercenaries are progressing towards the [CAR] towns of Bria and Ndele."
He did not specify how many soldiers the government planned to deploy.
Former colonial power France has also pledged its logistical and intelligence support to CAR.
Meanwhile, United Nations High Commissioner for Human Rights Louise Arbour called on Friday for immediate action to be taken to prevent a human rights catastrophe in Chad.
"I am deeply concerned that the horrendous violence that has been wracking Darfur is affecting Chad," she said in a statement.
According to the government, about 300 people have been killed in the violence since late October in eastern Chad.
Both Chad and Central African Republic have called for the deployment of international peacekeepers to secure their borders with Sudan
But Sudan has refused to permit a robust UN peacekeeping force to relieve an over-stretched African Union contingent in Darfur.
It is hoped Thursday's agreement on a joint UN and African Union peacekeeping force for Darfur could ease the situation.
Chad's army has been unable to stop attacks in the east
In April, Chad rebels reached the capital, N'Djamena, before being repulsed.
Sudan denied claims it had backed Chad's rebels, while Chad denied supporting the black African rebels in Darfur.
Eastern Chad and Darfur have a similar ethnic make-up.
Some two million people have been displaced in Darfur and at least 200,000 are estimated to have died in the three-and-a-half year conflict.
Sudan's government says it is disarming Arab militias, known as Janjaweed, who have been accused of carrying out genocide on its behalf.
1. Chad says Sudan government-backed militias are attacking villagers in Chad. Some 200,000 Darfur refugees are also in Chad
2. Sudan accuses Chad of backing the Darfur rebels
3. Chad says it will send troops to help CAR fight the rebels
4. CAR says Sudan backs rebels who have seized towns in CAR