"Voter identification is a politically divisive issue, and rules in some states can present obstacles, particularly for low-income voters, racial and linguistic minorities and Native Americans," the release said.
OSCE also stressed that international observers were faced with restrictions in 12 US states. "Election observation is regulated by states, and restrictions on election day observation by international observers were in place in 12 of these," the release said.
Meanwhile, International observers saw no signs of foreign interference in the US midterm elections. "We did not see any evidence of that," OSCE special coordinator George Tsereteli told reporters when asked whether they saw any signs of foreign meddling in the midterm elections.
According to the latest preliminary results of the midterm elections, Democrats took control of the House of Representatives, but Republicans managed to secure their hold on the Senate.
Tuesday's vote was only the third time since 1962 that a sitting president picked up gains for his party in the Senate during a midterm election. The Republicans in previous years picked up two Senate seats during the 2002 midterms under President George W. Bush, and flipped two seats in 1970 under President Richard Nixon.
Several US Senate races remain too close to call, but so far, Republicans have registered a net gain of three Senate seats in this year's vote. Of the races that have been called, Republicans now hold 52 seats, and Democrats control 45 while three races are still too close to call.