Chad's military said it had carried out air strikes against Boko Haram bases in Nigeria in retaliation for twin suicide bombings in Chad this week that killed at least 34 people, but the announcement was strongly denied by Nigeria.
The air raids caused heavy human and material damage to six of the Islamist militants' bases, Chad's military said late on Wednesday, without providing further details.
Nigerian authorities rejected reports that the attacks had taken place on its soil, saying they were likely instead to have been in neighbouring Niger.
"The claim that the Chadian military have conducted air strikes against six terrorist camps in Nigeria is not correct," said military spokesman Major General Chris Olukolade. In recent weeks Nigeria said Boko Haram had been forced out of most of the areas it once controlled in northern Nigeria.
A few hours after Chad's announcement, Boko Haram militants attacked two villages in neighbouring Niger's southern region of Diffa, security sources said.
The attackers drove into the villages in the Gueskerou area, along the banks of the Komadugu River which separates Niger and Nigeria, in cars and on motorbikes and shot residents before setting fire to the thatched houses where others were hiding.
"In all, at least 30 were killed. Some of them died when the houses were set alight," said one of the security officials. He said he expected the death toll to rise as a number of survivors had suffered serious burns.
By mounting two major attacks outside its northern Nigerian stronghold in a few days, Boko Haram has demonstrated its ability to strike back in defiance of the coalition of regional armies seeking to stamp them out.
Chad has been a driving force behind the regional campaign, which has inflicted a series of defeats on Boko Haram since January.
Monday's simultaneous suicide attacks on a police headquarters and a training school in N'Djamena were the first of their kind in Chad.
Authorities in Chad have said four Boko Haram fighters were among the dead and at least five suspects have been detained in connection with the attacks, but no one has claimed responsibility for the bombings.
"Our defence and security forces will hunt down without mercy these terrorists without faith or law, so that spilling the blood of Chadians will not go unpunished," said Wednesday's written statement by army spokesman Colonel Azem Bermendoa.
Chad has announced measures including a ban on head-to-toe burqas and turbans to tighten security in the capital, home to the headquarters of a 3,000-strong French military mission.
A Reuters correspondent in N'Djamena said he had not seen any women wearing burqas on the streets since Wednesday's announcement.