Lagos - Nigeria's anti-graft agency on Thursday said it has arrested a former political associate of President Muhammadu Buhari as part of an ongoing corruption probe into allegedly bogus arms deals.Lawal Jafaru Isa, a former Kaduna state military governor under general Sani Abacha, was arrested late on Wednesday at his Abuja residence, the Economic and Financial Crimes Commission told AFP.He is the head of state's first party ally arrested in the probe.The retired brigadier general was the Kano state governorship candidate for the Congress for Progressives Change (CPC) in the 2011 election. Buhari was the party's presidential candidate.The CPC and three other parties merged in 2013 to form the All Progressives Congress (APC). Buhari was the APC candidate at elections last March, beating incumbent Goodluck Jonathan."It is true that he [Isa] has been arrested," said EFCC spokesperson Wilson Uwujaren. "His arrest is linked with the current investigation on the former national security advisor, Colonel Sambo Dasuki."No further details were given about why Isa was arrested, although he is said to be close to Dasuki, who served under Jonathan.Dasuki is alleged to have awarded about $2bn in bogus deals for fighter jets, helicopters, weapons and ammunition for the military battling Boko Haram Islamists in northeast Nigeria.But the hardware failed to materialise and the money was instead diverted to Jonathan's Peoples Democratic Party (PDP) to finance his re-election bid, according to the EFCC.Dasuki and several other high-ranking suspects, including a media mogul and a former junior finance minister, have pleaded not guilty to corruption charges.The PDP has accused Buhari and the APC of conducting a witch-hunt after a string of senior party figures, including its acting chairman and spokesman, were arrested in connection with the case.