Two more Turks tested positive for the deadly H5N1 strain of bird flu in preliminary tests, the government said Thursday, bringing the total number of human infections to 18. Both victims were from the stricken southeast, and had been in contact with infected birds, officials said.

A Turkish lab also determined that last week's third bird flu death involved the H5N1 strain, the Health Ministry said, as authorities stepped up the precautionary slaughter of thousands of birds in an effort to keep the outbreak in check.