Iran's Guardian Council is allowing 200 reformist candidates of more than 3,500 blacklisted a week ago to stand in next month's elections.
Protesting MPs vow to remain at parliament until the row is resolved
Abbas Kadkodaye of the conservative legal body said it was speeding up the review process after an appeal by Supreme Leader Ayatollah Ali Khamenei.
The Council's decision has plunged Iran into crisis provoking accusations that hardliners are trying to rig the polls.
President Khatami's political party has threatened to boycott the elections.
"After the order was given by the Supreme Leader, we have been obliged to speed up our work," said Mr Kadkodaye on the Guardian Council website.
"So far 200 candidates have been approved".
He did not specify which candidates.
Mr Khamenei intervened at the weekend, urging the 12-member body - which screens all laws and candidates - to re-examine its blacklist.
"The Guardian Council has enough time to review the cases carefully... to prevent the violation of anyone's rights," he said at the time.
On Monday, President Khatami's party, Association of Combatant Clerics, raised the pressure by threatening to boycott elections scheduled for 20 February.
"If urgent measures are not taken to settle the current problem, which prevents free competition between legal political views, there is no further reason for the Association to take part in the parliamentary election," it said in a statement.
President Khatami's party has threatened to boycott the election
Earlier this month, the electoral vetting arm of the Guardian Council disqualified more than 3,500 of the 8,000 or so candidates.
Since that time, around 80 of the banned MPs have refused to leave the Iranian parliament, the Majlis, in protest at their being banned from re-election.
While their candidacies received the backing of Ayatollah Khamenei, he warned the Guardian Council not to retreat in the face of people who wanted to resort to bullying tactics, a tacit reference to the protest itself.
The Guardian Council on Sunday reiterated its defiant posture in a rare news conference, saying it would not bow to pressure to retract the candidate vetoes.
Spokesman Ebrahim Aziz said its members would "not succumb to any pressure or propaganda", but added that they would follow Ayatollah Khamenei's request to review the cases.
The Council has until 30 January to complete its review.
Those still disqualified have another chance to appeal before campaigning starts on 12 February.