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Until Basra , U . S . and British troops had encountered little resistance , even when they seized nearby Umm Qasr , and moved to secure key oil fields .
 troops: attacker; Umm Qasr: place
Given event type and trigger, please tell me the arguments of all the listed option. Output format is "name1: role1; name2: role2". 
Event type: attack 
  Option: victim, attacker, place, target, instrument 
Text: {0} 
Answer:
 troops: attacker; Umm Qasr: place