Sudan has accused Chad's Deby of being involved in a recent attack on Khartoum [AFP]
The alleged raids, the latest of which Khartoum says took place on Saturday, come days after Chad said Sudan had sent armed groups across its border.
Sudan has accused neighbouring Chad of launching a third air raid on its territory, a day after it said Ndjamena was responsible for two other bombings.
"There was another air strike this morning at around 10am," Ali Youssef Ahmed, head of protocol at Sudan's foreign ministry, said on Saturday, a day after the first two alleged raids occurred.
"This aggression continues [and] this makes the situation graver."
'Act of war'
Ahmed on Friday said that that there had been casualties in the first two alleged raids, calling them an "act of war".
Ahmed declined to comment on whether Sudan planned to retaliate, saying: "We are considering all options."
Mohammed Vall, Al Jazeera's correspondent in Khartoum, said the Sudanese government has consulted ambassadors of the permanent members of the UN Security Council, complaining of Chad's behaviour.
"There has never been an open war between the two countries, but this is a very serious development," he said.
"The Sudanese authorities have made it very clear that they reserve the right to retaliate."
Chad denial
Chad late on Friday hit back at Sudanese accusations saying Khartoum was "the robber who cries thief".
Mahamat Hissene, a government spokesman, told reporters that Chad "is surprised to learn that the regime in Khartoum is protesting against action by the Chadian air force on Sudanese territory".
Hissene said that any confrontations would be "simply the consequence of the attack on Chad organised by Sudan, using mercenaries armed, trained, financed and directed by satellite by the Khartoum regime".
Both countries have regularly accused each other of backing fighters bent on overthrowing their respective governments.
Ahmed said Sudan's foreign ministry had called in Chad's ambassador to demand an explanation for the two sorties and had informed the Khartoum-based ambassadors of the five permanent members of the UN Security Council.
Three warplanes
Chad accused Sudan of backing an armed incursion into its territory last week, after the two countries had signed a pact in Doha, Qatar.
They had agreed in that deal to normalise relations and reject any support for rebel groups hostile to either of them.
Chad said it had stopped the advance, after clashes that killed 125 fighters.
Sudan denied involvement in the raid, saying it was a confrontation between Chad's government and "opposition groups".
Chad and Sudan resumed shaky diplomatic ties in November after cutting them in May 2008.
Sudan has accused Idriss Deby, the president of Chad, of being involved in an attack on the Sudanese capital by Darfur rebels on May 11, 2008.
Sudan blamed Chad on Sunday of launching an air strike on its territory, a day after accusing the country of mounting two other raids.

"This morning at 10.30 local time 0.730 GMT, another visit took place on the same location and using the same method," said Othman al-Aghbash, a spokesman for the Sudanese army.

Sudan also accused Chad earlier on Friday of launching a pair of airstrikes  into Sudanese territory. Chad promptly dismissed the accusations, claiming that Sudan was "the robber who cries thief."

Ali Youssef Ahmed, the head of the Sudanian foreign ministry, called the Friday air strikes an "act of war". He did not comment on whether Sudan was considering to retaliate to the alleged attacks, only saying that "we are considering all options."

A spokesman for the Chadian government told reporters that "is surprised to learn that the regime in Khartoum is protesting against action by the Chadian air force on Sudanese territory". A confrontation would be "simply the consequence of the attack on Chad organised by Sudan, using mercenaries armed, trained, financed and directed by satellite by the Khartoum regime", he said.