The lawyers representing Libyan military commander Abdel Hakim Belhadj say they have sent Labour MP Jack Straw a letter to ask him to respond to reports that he personally signed documents that allowed Belhadj to be sent back to Libya in 2004.
Straw is facing similar legal action from fellow Libyan and Gaddafi opponent Sami Al Saadi who was also sent back into the hands of the regime in 2004.
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163,000 French and 143,000 German soldiers were killed in the 10-month battle in 1916.
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The fire broke out on Sunday morning at the home for 35 residents in Litochki, a village 25 miles north of Kiev.