Biden sidesteps questions about his son's foreign business dealings but promises ethics pledge originally appeared on abcnews.go.com

Democratic presidential candidate Joe Biden declined to answer questions on the campaign trail this week about his son's overseas business dealings in countries where the then-vice president was conducting diplomatic work, an issue his political opponents have already begun to wield against him as he wades into the 2020 presidential campaign.

More than once, after his father engaged in diplomacy on behalf of the United States in foreign countries, Hunter Biden conducted business in the same country. At two separate campaign stops on Monday, Biden avoided questions about his son while his staff blocked reporters from approaching the candidate.

Biden's campaign did provide ABC News with a statement saying the former vice president has always adhered to "well-established executive branch ethics standards," adding that if Biden wins the White House he will issue an executive order to "address conflicts of interest of any kind."

"This process will be set out in detail in the executive order," the statement reads, "that President Biden would issue on his first day in office."

The ethics pledge follows renewed questions about a pair of overseas business opportunities involving Hunter Biden – one in Ukraine, another in China – that already have begun to generate political attacks from Joe Biden's conservative critics. Ethics experts interviewed by ABC News said these are legitimate questions about possible past and future conflicts of interest.

PHOTO: In this file photo, World Food Program USA Board Chairman Hunter Biden (L) and Vice President Joe Biden attend the World Food Program USA's Annual McGovern-Dole Leadership Award Ceremony on April 12, 2016 in Washington. (Teresa Kroeger/Getty Images for World Food Program USA, FILE) More

In April of 2014, the then-vice president led a U.S. delegation to Kiev tasked with rooting out corruption and advocating for Ukraine to diminish its reliance on Russian oil. The Obama administration had pledged aid money to support a fledgling Ukrainian administration recovering from a revolution that ousted the country's previous leader.

(MORE: Joe Biden is entering the 2020 field. Here's everything you need to know.)

"You have to fight the cancer of corruption that is endemic in your system right now," Biden told the Ukrainian parliament during the first of several post-revolution visits to the country. "And with the right investments and the right choices, Ukraine can reduce its energy dependence and increase its energy security."

Within weeks of his visit, Ukraine's largest energy producer, Burisma Energy, appointed Hunter Biden to a paid directorship on the firm's board.

Just months before, in December of 2013, there was a similar episode when the then-vice president led an Obama administration effort to tamp down tensions in the Far East. Hunter Biden disembarked from Air Force Two in Beijing alongside his father, ahead of a series of meetings between the vice president and several high-ranking members of China's ruling party. Upon his departure, Joe Biden called Chinese President Xi Jinping a "good friend."

Within weeks of that visit, Hunter Biden was doing business there, as a participant in a firm called Bohai Harvest RST. The corporation formed a novel Chinese-American investment partnership that involved such Chinese state-owned firms as the Bank of China. Reports at the time said they sought to raise $1.5 billion.

In response to questions from ABC News, Hunter Biden maintained that he and his father never talked about his overseas ventures.

PHOTO: In this file photo, Vice President Joe Biden, left, accompanied by daughter Ashley Biden, and sons Beau Biden and Hunter Biden, walks down the steps of Air Force Two upon their arrival in Lexington, K.Y., on Oct. 11, 2012. (Pablo Martinez Monsivais/AP, FILE) More

(MORE: Joe Biden's Son Hunter Biden Discharged From Navy After Positive Cocaine Test)

Story continues