WASHINGTON, July 16 (Xinhua) -- U.S. Democratic presidential hopeful Barack Obama on Wednesday said he'd like the world free of nuclear weapons and pledged to fight emerging threats posed by biological and cyber-terrorism.

    The Senator from Illinois made the remarks at a roundtable discussion on national security in West Lafayette, Ind.

    "It's time to send a clear message to the world: America seeks a world with no nuclear weapons," he said.

    "As long as nuclear weapons exist, we'll retain a strong deterrent. But we'll make the goal of eliminating all nuclear weapons a central element in our nuclear policy," Obama added.

    The remarks, delivered before a roundtable discussion with foreign policy experts, come before the presidential hopeful's scheduled trip to Europe and Mideast.

    It is the second day in a row that he focuses his speech on national security issues.

    Obama is trying to beat back the public perception that he is less experienced than his Republican rival John McCain when handling national security.

    Shortly after he concluded his remarks, the McCain campaign released a letter signed by 10 retired admirals and generals touting McCain's national security credentials.