In a TV advert which is to be broadcast during the Republican National Convention, The Mayor of San Diego, California, has spoken urging voters to support equal marriage for all.

In the video, which is set to air in Tampa, Florida, where the RNC is taking place next week, Jerry Sanders discussed his support for equal marriage, and said the Republican Party is “changing” on the issue of equal marriage.

He said: “In 2007, I announced my support for marriage equality for two reasons: family and freedom. As a republican I believe in conservative values, like responsibility and limited government.

“Marriage strengthens families, and we need more of that in this country, not less.”

Sanders was co-chair of a coalition, Mayors for the Freedom to Marry, which included seventy US Mayors who joined together in January with a view to increasing the pressure on President Barack Obama and to achieve full support of equal marriage rights nationwide.

The advert was produced as a joint venture by Freedom to Marry and the Human Rights Campaign. Chad Griffin, President of the Human Rights Campaign released a statement:

“While the GOP’s official position on marriage equality is stale to most Americans, there is a growing movement within the party heading inexorably toward fairness,”

This comes amidst a flurry of criticism of the party for their stance on equal marriage, both from within and outside the party. Just this week, Mitt Romney’s advisor was criticised for likening being gay to drug use, and polygamy.

The Democratic Party are expected to come out in support of equal marriage at their National Convention in September. A gay pride event being held in the same city aims to drum up support and awareness ahead of the convention.