(Adds diplomat, U.S. officials, HRW, context)
By Ellen Francis
BEIRUT, Oct 10 (Reuters) - A senior Kurdish official warned on Thursday that Islamic State jihadists could break out of prisons in northeast Syria as fighting intensifies between Kurdish-led forces and Turkey.
Badran Jia Kurd told Reuters the number of security forces guarding the militants will dwindle as Turkish forces step up an offensive they launched at the border on Wednesday. U.S. officials have worried Islamic State detainees would sieze on such an opportunity for a prison break.
The Syrian Democratic Forces (SDF) hold thousands of the militants in prisons and tens of thousands of their relatives in camps, many of them foreigners. With the Kurdish YPG militia at its forefront, the SDF defeated jihadists across much of north and east Syria with U.S. air and ground support.
"This attack will definitely reduce and weaken the guarding system for those Daesh militants in the prisons," Jia Kurd said, using the Arabic acronym for Islamic State.
"This could lead to their escape or to behaviors that may get out of the control of the security forces," added Jia Kurd, adviser to the Kurdish-led authority in the SDF region.
"The number of forces guarding the prisons is reduced the more the battles intensify. This poses a grave danger."
The SDF says it has 70,000 foreigners in custody from around 60 nationalities, including militants, their wives and children, on top of thousands of detained Syrian and Iraqi fighters.
Kurdish leaders have said they do not have the resources to bear this burden alone, pleading with governments to take their citizens back but most have turned a blind eye. U.S. officials have said as many as around 2,000 of the Islamic State militants in detention are foreigners.
A U.S. official said the U.S. military took custody on Wednesday of two high-profile British Islamic State militants that the SDF was holding and moved them out of Syria. The official said the individuals were being held in a secure location but offered no further details.
Turkey's offensive into northeast Syria kicked off days after U.S. forces withdrew from part of the border, opening up a dangerous new phase in Syria's more than eight-year-old conflict.
TURKEY SEEKS TO ASSUAGE CONCERNS
Turkish President Tayyip Erdogan sought to assuage concerns from world powers on Thursday that his operation runs the risk of an Islamic State jail break amid the chaos. He said he guaranteed jihadists will not have a presence in northeast Syria after Turkey completes its offensive.
The border strip which U.S. forces vacated this week, and which is believed to be the focus of Ankara's incursion, is a nearly 100-km (62-mile) stretch between the Syrian towns of Tel Abyad and Ras al-Ain. It does not include prisons.
A diplomat following Syria said the SDF was unlikely to release prisoners on purpose.
"We can't rule out unrest in the IDP (Internally displaced persons) camps to make life more difficult for the SDF, or ISIS fighters trying to bust people out...We are watching it closely, we don't think they will open the gates. That is not their style and would be self defeating," the diplomat said.
"The SDF know how important this issue is to the international community - and some of the reports coming out are trying to create an international feeling of crisis around the issue of the ISIS detainees and their families."
Human Rights Watch said this week the SDF has held thousands of men and boys in severely overcrowded schools and other buildings on charges of having joined Islamic State. It said the Turkish incursion highlights the urgent need for countries to repatriate their citizens.
"No one is accepting responsibility for them," the U.S.-based rights group said, calling for urgently improving prison conditions and ensuring lawful detention.
Kurdish-led authorities accused Turkey of bombing a prison holding foreign jihadists in Qamishli city on Wednesday night. Ankara has yet to respond to the accusation.
The SDF has halted operations against Islamic State because of the Turkish offensive, two U.S. officials and a Kurdish source said. (Additional reporting by Tom Perry in Beirut and Phil Stewart in Washington; Writing by Ellen Francis Editing by Peter Graff)