Sri Lanka, Jan. 12 -- Iran said on Monday it is keeping communications open with the U.S. as President Donald Trump weighed responses to a deadly crackdown on nationwide protests, which pose one of the stiffest challenges to clerical rule since the 1979 Islamic Revolution.

Trump said on Sunday the U.S. may meet Iranian officials and he was in contact with Iran's opposition, while piling pressure on its leaders, including threatening possible military action over lethal violence against protesters.

U.S.-based rights group HRANA said it had verified the deaths of 544 people - 496 protesters and 48 security personnel, with 10,681 people arrested since the protests began on December 28 and spread around the country.

Reuters was unable to i...