Egypt's stock exchange made its largest one-day decline in two months on concerns over the presidential election outcome, while most Gulf markets slipped on Sunday amid uncertainty over a possible Greek exit from the euro.

Cairo's index fell 3.5 percent, its biggest one-day drop since 25 March, after two of the most divisive candidates emerged as the likely contenders of next month's runoff vote.

State television said the Brotherhood's Mohamed Morsy led this week's vote with 26.4 percent against 23 percent for ex-air force chief Ahmed Shafiq, according to preliminary results.

"Some investors are afraid that because we now have the two extreme elements confronting one another, then the coming period will not be calm," said Osama Mourad, chief executive of Arab Finance Brokerage.

Real estate developer SODIC booked the largest losses, down 9.7 percent, and investment bank EFG Hermes tumbled 9.2 percent.

Mourad said investors are also concerned about possible repercussions of the verdict, due on 2 June, in the highly charged trial of former President Hosni Mubarak.