The United States is ready for direct negotiations with Iran, U.S. special envoy Rob Malley said in a statement late Thursday.

"This is the best solution to this complicated issue," he added, referring to Iran's nuclear program.

Sanctions have been reimposed on Iran after then-U.S. President Donald Trump quit the nuclear agreement.

Under the pact, Iran agreed with major powers that it would curb its nuclear program in return for the lifting of international economic sanctions.

About a year after Washington reimposed sanctions, Iran started violating the nuclear restrictions. Tehran denies seeking nuclear weapons.

Talks are being held in Vienna on reviving the deal but they have shown little progress.

If there is no progress in these talks, the United States could send delegations to several other countries to tighten the economic pressure on Iran, the Wall Street Journal reported.

U.S. and Israeli defense chiefs were expected on Thursday to discuss possible military exercises to prepare for a worst-case scenario of destroying Iran's nuclear facilities if diplomacy fails, a senior U.S. official told Reuters.