CASTRIES, St Lucia, May 1 (Reuters) - Antigua and Barbuda Prime Minister Gaston Browne won a landslide election victory late on Thursday, securing a fourth term after a campaign dominated by the economy and concerns over U.S. visa restrictions.

Browne's Labour Party increased its majority by winning 15 seats in the 17-seat parliament, according to preliminary official data. The opposition United Progressive Party, seen as its main challenger, won only one seat.

"We are humbled and honored by your support and confidence," the Antigua and Barbuda Labour Party said on social media.

Browne, a 59-year-old former banker and businessman who has led the Labour Party since 2014, campaigned on economic stability and investment-led growth, pointing to a post-pandemic recovery in tourism and to infrastructure expansion.

The political debate was mostly dominated by Washington's decision in January to suspend visa processing for Antigua and Barbuda nationals - a major blow for locals who regularly travel to the United States for work. 

Washington raised concerns over a program where foreigners can secure citizenship in the Eastern Caribbean twin-island state through investment. It argued that criminals could exploit the scheme to get into the United States.  

Browne's administration said it was working with the U.S. and that it has already brought in reforms to make the Citizenship by Investment Program more robust and transparent.

The Labour Party called the general election last month, two years ahead of schedule, saying it needed a new mandate at a time of international crisis. It had a nine-seat majority in the last parliament.

There will be a second vote count on Friday to confirm the results of the general election that has been monitored by international observers.