Stock markets in the United Arab Emirates have fallen sharply for the second day because of continuing concern over a possible default in its debt by the investment company, Dubai World. In early trading, the markets in Dubai and Abu Dhabi were down by about six per cent. Yesterday, the Dubai World announced that it has begun talks with bankers on the restructuring of 26 billion dollars of the firm's debt. Earlier, the government in Dubai confirmed it will not guarantee the conglomerate's debt.