Idriss Deby, the president of Chad, has accused neighbouring Libya of not doing enough to stop Chadian "mercenaries" he says are being trained in western Libya.
Speaking to Al Jazeera on Saturday, Deby said the fighters had set up a training camp in Benghazi from where they could seek to destabilise his country.
"Libya is now infested with mercenaries. Camps are set up [for] them in Benghazi where Chadians are assembled and recruited.
"I know who is directing and commanding those mercenaries. I call on Libyan authorities to take every possible measure to spare Chad from new plot being originates in their country,"
Speaking to Al Jazeera by telephone, Ibrahim Dabbashi, Libya's ambassador to the UN, said Deby's claims lacked credibility.
"The president of Chad used to be a good friend of [Muammar] Gaddafi," he said.
"He [Deby] was blackmailing Gaddafi in the past to get the money to support the regime ... Maybe [Deby] now is looking for a kind of support outside his country."
The two nations have long had a tense relationship.
Gaddafi, the former leader of Libya, long aimed to annex a strip along the border of the two countries known as the Aouzou strip.
In the nine years between 1978 and 1987, Libyan forces entered Chad on four seperate occasions.
Under Libyan control, residents of the uranium-rich region were offered Libyan citizenship.