Briton Simon Chase, who was among the victims in a suicide attack in Kabul, had been living with his fiancee in County Londonderry, Northern Ireland.
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Navy officials say they have received seven short satellite calls which are though to have come from the submarine.
The President is to meet with with the army commander who put him under arrest as he resists calls for him to stand down.
The military had hoped for a smooth transition from the old leader, but Mugabe looks like he means to stay put.