President Barack Obama insisted Wednesday that higher taxes for the wealthy had to be a part of any deal on averting the fiscal cliff looming at year-end.

"We cannot afford to extend the Bush tax cuts for the wealthy," he said, while saying tax breaks for middle class families should stay in place.

Speaking in his first formal press conference in eight months and his first since being re-elected last week, Obama said no one has provided any evidence so far to indicate that classified information was disclosed as a result of the sex scandal that cost retired General David Petraeus his job as head of the Central Intelligence Agency.

He also said he is not supposed to meddle in the Federal Bureau of Investigation's probe of the Petraeus matter, and he will not prejudge the investigation's results.

"General Petraeus had an extraordinary career," Obama said, but by Petraeus' own assessment, the former top commander of US troops in Afghanistan no longer met the standards to keep running the CIA.

Obama added he is confident he can work with the US Congress to reform immigration laws, and expects a bill will be introduced soon after his January inauguration.

The bill should include a pathway to legal status for illegal immigrants already in the United States, including people brought to the United States illegally as children, as well as strong border security measures and penalties for companies that hire undocumented workers, Obama said.

Obama did not however comment on the recent military operation launched in Gaza Strip killing top Hamas military commander Ahmed al-Jaabari.