More former detainees held in the U.S. Guantanamo Bay prison have returned to terrorism after they were released, said the Pentagon on Wednesday.

Pentagon Press Secretary Geoff Morrell told reporters that the latest figure shows the number of former Guantanamo prisoners retaking terrorism was still on increase, but he did not disclose the exact number.

According to the defense department, about 14 percent of former detainees have joined or were suspected of joining terrorism as of April 2009, compared to 11 percent in December 2008.

The U.S. government is expected to miss the Jan. 22, 2010 deadline it has set to close the Guantanamo prison.

President Barack Obama on Tuesday announced that his administration had to suspend the transfer of additional Yemeni detainees to their home country, since the al-Qaeda branch in the Arabian Peninsula is operating actively in the country.

The group has claimed responsibility for the attempted bombing of a U.S. international flight on Christmas Day, and at least two of its members used to be held in the Guantanamo prison.

Currently, there are 198 prisoners left at the Guantanamo prison, and about 90 of them are Yemeni, according to the Pentagon.