"The threats and the use of economic pressure which we have seen over the last year are simply unacceptable," Germany's outgoing foreign minister told an OSCE security meeting in the Ukrainian capital Kiev on Thursday.
"The people in Ukraine want to decide their future themselves," he said, noting he was "worried" by a police crackdown on protesters.
On Wednesday, at the start of his visit to the crisis-gripped country, he said the gates of Europe were still open for Ukraine, after mass protests against the government's decision to walk away from a deal with the European Union.
"The gates of the European Union are still open. Ukraine has to be on board in Europe and the offers from Europe are still valid," Westerwelle told reporters, before heading to the heart of the protests on Independence Square.
He met boxing champions Wladimir Klitschko and his brother Vitali in the capital and was given a tour of the protest by them.
Ukraine's biggest pro-democracy rallies since the 2004 Orange Revolution have demanded President Viktor Yanukovych's resignation over his rejection, under Russian pressure, of a pact seeking closer ties between the ex-Soviet state and the EU.