ISTANBUL, May 9 (Reuters) - Turkey’s currency weakened beyond 6.24 against the dollar on Thursday, hitting its weakest level in eight months amid concerns over the re-run of Istanbul’s mayoral election and tensions ahead of U.S.-China trade talks.

The lira fell as far as 6.2410 against the dollar at 0914 GMT, its weakest level since September 24, sliding nearly 1 percent from its close of 6.1790.

After weeks of appeals by President Tayyip Erdogan’s AK Party and its nationalist MHP ally, Turkey’s High Election Board (YSK) ruled on Monday for a re-run of the Istanbul mayoral election, which was narrowly won by the opposition.

Turkey’s main opposition party said on Wednesday it had formally requested the annulment of Erdogan’s mandate because the same flaws his AK Party alleged in the city’s March 31 mayoral vote occurred in last year’s national elections.

Investors fear that the decision to re-run the Istanbul election on June 23 will add nearly two months of uncertainty over Turkey’s plan to rebalance and stabilize the economy.