US President Donald Trump speaks to the press after announcing and initial deal with China at the South Lawn of the White House in Washington, DC before departing to Lake Charles, Lousiana to hold a campaign rally on October 11, 2019.

President Donald Trump defended his attorney Rudy Giuliani on Saturday after a media report revealed that federal prosecutors are investigating whether the former New York mayor broke lobbying laws in his dealings in Ukraine.

"So now they are after the legendary 'crime buster' and greatest Mayor in the history of NYC, Rudy Giuliani," Trump wrote on Twitter. "He may seem a little rough around the edges sometimes, but he is also a great guy and wonderful lawyer."

Investigators in Manhattan after examining Giuliani's efforts to undermine the American ambassador to Ukraine, Marie L. Yovanovitch, and if he broke laws in place to prevent foreign influence on the government.

The investigation of Giuliani raises the stakes of the Ukraine scandal for Trump, who is facing an impeachment inquiry for his dealings with the country.

The probe is tied to the case against two foreign-born Giuliani associates, Lev Parnas and Igor Fruman, who were arrested this week on campaign finance charges at an airport with one-way tickets out of the country. They were charged with conspiracy, lying to the Federal Election Commission and falsifying records.

The indictment also alleges they made illegal donations to a then-sitting U.S. congressman in order to evade federal contribution limits, and that Parnas had asked that congressman for assistance in getting the U.S. to remove Yovanovitch.

House Democrats leading an impeachment inquiry into Trump issued subpoenas to Parnas and Fruman on Thursday. The businessmen were ordered by leaders of three House committees to give documents and testify as part of the impeachment probe.

Giuliani has denied that he had any business dealings in Ukraine. However, he has acknowledged that he and the associates worked with Ukrainian prosecutors to collect potentially damaging information about Yovanovitch and other Trump targets, including former Vice President Joe Biden and his son.