"All those things, I think, are going to be very difficult," Biden told CNN in an interview Thursday after a senior US administration official claimed that Israel was behind the assassination.
"The bottom line is that we can't allow Iran to get nuclear weapons," Biden said, criticizing President Donald Trump for pulling the US out of the 2015 nuclear deal that Biden helped former President Barack Obama craft.
"He has pulled out to get something tougher, and what have they done? They've increased the ability for them to have nuclear material. They're moving closer to the ability to be able to have enough material for a nuclear weapon. And there's the missile issues," Biden argued.
The former vice president stressed that the US needs partners in its relations with Iran, suggesting that his administration could work together with Russia and China on many issues.
Amid unconfirmed reports that Trump might not attend his Jan. 20 inauguration ceremony, Biden said Trump should attend, partially to avoid pointing a negative picture for the rest of the world.
"It's important in the sense that we are able to demonstrate the end of this chaos that he's created, that there is peaceful transfer of power with the competing parties standing there, shaking hands and moving on," he said.
100 days of face masks
Biden also said he would ask Americans to wear face masks during his first 100 days in the office, which would be a drastic shift from Trump's often dismissive attitude towards the virus.
To make mask-wearing mandatory, Biden said he would use his authority in federal buildings and on airplanes and buses during interstate transportation, on top of issuing an order for masks to be worn.
Biden urged Americans to trust in an upcoming COVID-19 vaccine, adding he will be "happy" take the vaccine once chief medical advisor Dr. Anthony Fauci says it is safe.
"That's the moment in which I will stand before the public. People have lost faith in the ability of the vaccine to work," he said.
Economic stimulus
Biden, however, underlined the complexity of vaccine distribution, and urged the need for a relief bill to provide necessary funding.
Democrats earlier this week lowered their relief bill offer from $2.2 trillion to $908 billion to close the gap with Republicans' offer of approximately $500 billion, news Biden called "a good start" to bipartisan efforts.
"What's immediately needed is relief for people in their unemployment checks; relief for people who are going to get thrown out of their apartments after Christmas because they can't afford to pay the rent anymore ... People are really hurting. They're scared to death," he explained.
After a relief bill is passed, Biden pledged to work on passing an additional stimulus as well.