Paris - Chad faces an "explosive situation" in the runup to presidential elections in April, the country's opposition leader said on Wednesday, warning that its people will not accept a rigged result.The Sahel country, which remains poor despite starting to make money from oil exports, is in "an extremely tense political atmosphere," Saleh Kebzabo said during a visit to Paris following crippling nationwide strikes last week over President Idriss Deby's planned bid for re-election. "If there is electoral fraud, which we can fear, Chadians will not stay serene and calm... There will be a serious post-election crisis," warned Kebzabo, who has lost to Deby in two previous elections."Idriss Deby has never been democratically elected," said the head of the National Union for Development and Renewal (UNDR), who is among Deby's challengers in the April 10 polls."He has always used fraud, but this time that won't be possible" thanks to biometric voting cards, said Kebzabo, who held several ministerial portfolios under the longtime ruler."So that leaves fraud inside the polling stations," he said.Kebzabo made two unsuccessful presidential bids in 1996 and 2001, coming in third behind Deby, who has been in power for 26 years.Seized powerThe autocratic ruler modified the constitution in 2004, scrapping its two-term limit on presidential tenure, and won the following elections by a huge majority.Deby, 63, seized power in 1990 after toppling Hissene Habre, who is on trial at a special court in Senegal for crimes against humanity.Kebzabo boycotted polls in 2006 and 2011. Before joining the opposition, he was a minister in Deby's government several times between 1993 and 2001.Chad last month also saw an unprecedented wave of protests over a girl's brutal gang rape blamed on the sons of senior officials.Two demonstrators were killed when police broke up the protests.