(Reuters) - The nation's largest civil rights group, the NAACP, endorsed gay marriage on Saturday, giving a boost to the movement to legalize same-sex nuptials despite reservations expressed by some black ministers.

The National Association for the Advancement of Colored People passed the resolution at its board meeting in Miami "as a continuation of its historic commitment to equal protection under the law," the organization said.

"Civil marriage is a civil right and a matter of civil law. The NAACP's support for marriage equality is deeply rooted in the Fourteenth Amendment of the United States Constitution and equal protection of all people," Benjamin Todd Jealous, President and CEO of the NAACP, said in a statement.

The gay rights movement got a big boost last week when President Barack Obama said for the first time he supports gay marriage.

After he announced his decision, Obama held a conference call with at least eight black ministers, some of whom were skeptical, to explain his position, The New York Times reported.

Three state legislatures have voted this year to legalize gay marriage - New Jersey, Maryland and Washington state - although New Jersey Republican Governor Chris Christie vetoed the measure. In Maryland the law passed even though some black Democrats opposed it.

Six other states - New York, Connecticut, Vermont, New Hampshire, Massachusetts, and Iowa plus the District of Columbia - have legalized gay marriage, and a handful of others recognize so-called "civil unions."

"EQUAL MEMBERS OF SOCIETY"

There has been a steady increase in support for same-sex marriage. The Gallup polling organization said in a recent survey that 50 percent of American adults now are in favor of it.

"Americans' acceptance of gays and lesbians as equal members of society has increased steadily in the past decade to the point that half or more now agree ... that gay or lesbian couples should have the right to legally marry," Gallup said on its website. Continued...