Pakistani Taliban militants have freed a Chinese engineer held captive for nearly six months, officials said Sunday, as fears rose for the safety of an abducted American threatened with imminent death by his kidnappers. It was not immediately clear what prompted Long Xiaowei's release, including whether a ransom was paid or militants were freed in exchange, but the news that he was safe was a rare bright spot in a month of heightened security concerns for foreigners in Pakistan. Long's release came days before a visit to China by Pakistani President Asif Ali Zardari. Earlier this month, a Polish geologist held by Taliban fighters was apparently beheaded on a video obtained by news media and authorities and believed by the Polish government to be authentic. On Friday, the kidnappers of American UN official John Solecki threatened to kill him within 72 hours and issued a 20-second video of a blindfolded Solecki saying he was "sick and in trouble."