Defense Secretary Donald Rumsfeld has arrived in Thailand for meetings with top officials, after attending an Asian security conference in Singapore. Mr. Rumsfeld arrived Sunday and is expected to meet with Thai Prime Minister Thaksin Shinawatra and defense officials on Monday. Saturday at the security conference, Mr. Rumsfeld voiced concern over China's military buildup, saying it could threaten the security balance in Asia. He told defense ministers from 21 nations China has the third-largest military budget in the world. And he said China appears to be expanding its missile forces, despite the fact that no nation threatens China. He also said North Korea's nuclear ambitions threaten the security of the region, and China can make a key contribution in persuading Pyongyang to return to negotiations.