Embattled cloning pioneer Hwang Woo-suk insists his research team had five patient-specific stem cell lines, denying the allegation he had none.

In a Friday news conference at Seoul National University, Hwang said mildew polluted the stem cells during storage but that he has the source technology and can make them in two weeks.

He also said he asked Science magazine to retract his paper published in May not because of inaccuracy but due to degraded images from faulty stem cell photos and other "mistakes."

Apologizing to the public, he said his research will eventually prove the validity of his work.

Hwang said additional stem cells he made later were confirmed to have been switched with those at MizMedi Hospital in the recent verification process, asking authorities to look into the matter.