WASHINGTON (REUTERS) - The rebuilt cast-iron dome of the US Capitol, a soaring symbol of national unity since the 19th century, was formally completed on Tuesday after a US$60 million (S$84.9 million) overhaul that included repairing more than 1,300 cracks and weak spots.

The project was the first complete rehabilitation of the 88-metre-tall Civil War-era dome since 1960. It was finished in time for the inauguration of President-elect Donald Trump on Jan 20.

"It is the symbol of American democracy and a beacon of hope around the world, and we delivered," Architect of the Capitol Stephen Ayers said at a news conference.

The 150-year-old structure tops the home of the US Congress and can be seen throughout the capital. The Capitol is a major tourist site, drawing thousands of visitors daily.

When work began in January 2014, the dome was suffering from water leaks, cracks and corrosion so bad that rain gutters were clogged with rust chips, Ayers said.