The detainees were being held at Abu Ghraib and other jails run by the US military and Iraqi forces.
A US military spokesman in charge of detainee operations said all of the 2,500 inmates released are just suspected of being involved in the insurgency but have committed no violent crimes like bombing, killing, torture and kidnapping. More than 14,000 detainees remain in US custody.
There have been numerous releases from Abu Ghraib and other facilities since the April 2004 prisoner abuse scandal.
But both US and Iraqi authorities were eager to link the latest releases to the Maliki plan.
Meanwhile Kurdish MP Mahmud Othman said seven armed groups were holding talks with President Jalal Talabani about laying down their arms.
But he said they were demanding "that there must be a timetable for withdrawal of foreign forces and also their resistance to foreign forces must be legitimately recognised."
The US has confirmed that it is considering a plan to sharply reduce its 130,000 strong force by the end of 2007, but said it was just one option among many and was not "engraved in stone."
Insurgents reject reconciliation
But Al-Qaeda and other groups have discounted the reconciliation plan and said they will carry on with their campaigns of violence.
It is "a malicious project aimed at salvaging his crusader masters and their apostate lackeys," said the Mujahedeen Shura (consultative) Council, an eight-member coalition led by Al-Qaeda's Iraq branch.
"We are determined to carry on our jihad ... No reconciliation with the infidels," said a statement posted on a website normally used by the group.
The statement, whose authenticity could not be independently confirmed, called on "the mujahedeen brethren" to "persevere on the path of jihad" and not to be deceived by negotiations designed to lead to "surrender."
The plan was also rejected by the Islamic Resistance Movement, whose armed wing comprises mainly elements from Iraq's dissolved former ruling Baath Party.
A statement said Mr Maliki's plan is meant essentially to uphold the legitimacy of his government, which was "created by the (US) occupation," and "ignores the main problem, namely ending the occupation, the major demand of all Iraqi resistance groups.
Ansar as-Sunna, another Al-Qaeda linked group, rejected the plan, calling Mr Maliki an "apostate."