KIEV, Jan. 12 - U.S. Vice President Joe Biden will fly to Kiev on Sunday on a farewell visit by one of Ukraine's strongest political supporters, as the country looks forward with apprehension to the new administration of Donald Trump, Reuters reported.

Biden, whose visit was announced by the office of President Petro Poroshenko, has been the front man for U.S. policy towards Ukraine since street protests in 2013-2014 forced a Russian-backed leader to flee and the pro-Western opposition took over, promising sweeping reforms whose delivery has been patchy.

The United States has invested heavily in the reform process, providing over $3 billion in economic assistance. It has imposed sanctions against Russia for annexing Ukraine's Crimean peninsula and backing separatists in a conflict in the east of the country.

Biden has been closely involved, visiting Ukraine four times since the change in power and maintaining regular telephone contact with Poroshenko and the prime minister.

Officials in Ukraine have expressed concern that U.S. support could wane following the Jan. 20 inauguration of Donald Trump, who has voiced admiration for Russian President Vladimir Putin and a desire to improve ties with Moscow.

Biden, who last year promised the "unwavering support" of the United States for Ukraine, has nevertheless chastised officials for lackluster reform efforts, warning that endemic corruption risks undermining international will to maintain sanctions on Russia.

During Biden's last visit to Kiev in December 2015, he made an impassioned speech to the Ukrainian parliament, saying lawmakers needed to do more in "a historic battle against corruption."

Meanwhile, senior U.S. Republican and Democratic senators plan to introduce legislation seeking to impose a wide range of sanctions on Russia over its cyber activities and actions in Syria and Ukraine.

The legislation is sponsored by 10 senators - Republicans John McCain, Lindsey Graham, Marco Rubio, Ben Sasse and Rob Portman and Democrats Ben Cardin, Robert Menendez, Jeanne Shaheen, Amy Klobuchar and Richard Durbin.

The bipartisan support increases the measure's chances of being passed by the Republican-led Congress. A House of Representatives aide said Russia sanctions legislation also was being prepared in that chamber.

The legislation would probably impose visa bans and freeze the assets of people "who engage in significant activities undermining the cyber security of public or private infrastructure and democratic institutions" or aids such activities. (rt/ez)