ANKARA, Turkey (CNN) --The U.S. troops vote by Turkey's parliament Saturday has been declared null, and the issue must now face a second vote -- which is expected to be rescheduled.

Doubt quickly clouded initial news that the Turkish parliament had approved on Saturday the measure, allowing the United States to deploy some 62,000 troops on Turkish soil in preparation for a possible war with Iraq.

Opposition leaders challenged the vote, saying that it was not approved by a majority of the parliament's membership.

The vote was 264 in favor, 251 against, and 19 abstaining. With 534 ministers present, a "yes" vote of 268 was needed, according to the opposition.

Opposition members were said to have walked out of the session.

The proposal has little popular support -- hundreds of thousands of Turks protested on the streets of Ankara, and public opinion polls show that more than 90 percent of the population opposes war.

But the matter has not been so clear-cut for Turkish leaders.

The United States has offered $6 billion in economic aid to offset fears that war could be devastating to Turkey's economy. Refusal to participate could have severely limited Turkey's role during a war and in a post-war Iraq.

U.S. ships carrying troops are waiting off shore and out of sight of the Turkish port of Iskenderun. U.S. officials have said they were confident Turkey would be the point of origin for a northern front in a war with Iraq.