Indonesia has detained 24 tugboats and barges carrying granite chips to Singapore, potentially threatening construction, a month after it banned all sand exports to its neighbor. Singapore Foreign Minister George Yeo said the 24 vessels, most of which fly the Singapore flag, were detained by Indonesian officials on Monday morning. Singapore’s construction sector is booming after years in the doldrums, although Indonesia’s ban on sand exports has worried investors that the recovery may be halted by tight sand supplies. Relations between Singapore and Indonesia have soured this year amid a diplomatic dispute over Jakarta’s decision to ban sand exports to the city state.