Iran has resumed 20 percent uranium enrichment at an underground nuclear facility, the government said on Monday, breaching a 2015 nuclear pact with major powers and possibly complicating efforts by U.S. President-elect Joe Biden to rejoin the deal.

The breach coincides with increasing tensions between Iran and the United States in the final days of President Donald Trump's administration.

Tehran started violating the accord in 2019 after Trump withdrew from the pact and re-imposed U.S. sanctions that had been lifted.

Monday's step was one of many mentioned in a law passed by Iran's parliament last month in response to the killing of the country's top nuclear scientist, which Tehran has blamed on Israel.

Such moves by Iran could hinder attempts by the incoming Biden administration to re-enter the agreement.

U.S. intelligence agencies believe Iran had a secret, coordinated nuclear weapons program that it halted in 2003. Iran denies ever having had one.

Israeli Prime Minister Benjamin Netanyahu said Monday, Iran's increased enrichment of uranium was aimed at developing nuclear weapons... and Israel would never allow Tehran to build them.