U.S. stocks declined on Thursday, with the benchmark indexes recording their worst session since July 31, as Apple tumbled on glitches tied to its new smartphone and as investors considered a proposal in Russia that would let its courts seize foreign assets.

"That would signal a threat from the Kremlin that the Russian-U.S.-Europe conflict economically might take a turn for the worse. They are signaling that unless concessions or negotiations take place, we're prepared to do this," said Jim Russell, senior equity strategist for US Bank Wealth Management.