File photo taken on May 18, 2019 shows former U.S. Vice President Joe Biden attending a campaign rally in Philadelphia, the United States. (Xinhua/Liu Jie)

The certification cemented Biden's victory in the key battleground state, which would give its 20 Electoral College votes to the former vice president and his running mate Kamala Harris.

WASHINGTON, Nov. 24  -- The U.S. state of Pennsylvania on Tuesday certified the presidential election results for Democrat Joe Biden.

Governor Tom Wolf tweeted that the Pennsylvania Department of State "certified the results of the November 3 election in Pennsylvania for president and vice president of the United States."

"As required by federal law, I've signed the Certificate of Ascertainment for the slate of electors for Joe Biden and Kamala Harris," the governor added.

The certification cemented Biden's victory in the key battleground state, which would give its 20 Electoral College votes to the former vice president and his running mate Harris, senator from California.

Michigan and Georgia, two other swing states, have also certified Biden's victory. U.S. media have projected that Biden has won 306 Electoral College votes, crossing the 270-vote threshold for clinching the White House.

President Donald Trump has yet to concede defeat. His campaign on Monday appealed a lawsuit seeking to block Pennsylvania's certification that was tossed out by a federal judge over the weekend.