Just two days ahead of a second round of talks on restoring diplomatic ties frozen for five decades, Cuba and the United States on Wednesday staked out competing demands to ensure progress.

Cuban officials demanded that as a preliminary step to renewing relations, Washington must remove the island from its list of state sponsors of terrorism.

The United States and Iran have a "mutual interest" in defeating the Islamic State group but the long-time foes are not cooperating to do so, Secretary of State John Kerry said Wednesday.

"They are totally opposed to ISIL and they are in fact taking on and fighting and eliminating ISIL members along the Iraqi border near Iran and have serious concerns about what that would do to the region," Kerry told lawmakers, referring to IS by another acronym.

Iran is "forever" banned from building a nuclear weapon under an existing international treaty, top U.S. diplomat John Kerry said Wednesday, seeking to dismiss fears that limits on its program imposed in a new deal may eventually be lifted.

"Please understand, there is no reduction (of restrictions) at any time that permits Iran to build a nuclear weapon," Kerry told U.S. lawmakers when pressed whether a deal with Tehran would eventually allow them to develop atomic arms.

Lawyers for WikiLeaks founder Julian Assange said Wednesday they filed an appeal to Sweden's Supreme Court seeking to quash the 2010 warrant for his arrest on accusations of rape and molestation.

Assange lawyer Per Samuelsson said he lodged the appeal with Sweden's top court Wednesday afternoon to end the stand-off in which the WikiLeaks founder remains holed up Ecuador’s embassy in London to avoid arrest and extradition, while Swedish prosecutors refuse requests he be questioned there.

Three New York residents from Kazakhstan and Uzbekistan have been arrested for allegedly trying to join the Islamic State (IS) group fighting in Syria, officials said Wednesday.

Abdurasul Hasanovich Juraboev, 24, Akhror Saidakhmetov, 19, and Abror Habibov, 30, have been charged with attempt and conspiracy to provide material support to a foreign terrorist organization.

South Africa has launched an investigation into the leak of espionage secrets to an international television news channel and a British newspaper, the state security minister said Wednesday.

"A full investigation has been launched into the purported leakage," Minister David Mahlobo said in a statement.

Iran denied Wednesday that it has played any part in a Shiite militia's power grab in Yemen, an accusation leveled by U.S. Secretary of State John Kerry.

Speaking to U.S. lawmakers Tuesday, Kerry said "critical" support of the Huthi militia by Shiite-dominated Iran "contributed" to the collapse of Yemen's government.

The United States has condemned the abduction by the Islamic State group of dozens of Assyrian Christians in Syria and demanded their immediate release.

It was the first mass kidnapping of Christians in the war-torn country.

U.S. Secretary of State John Kerry will address the U.N. Human Rights Council in Geneva next week, the U.N. said Wednesday, confirming he will be in Switzerland as new Iran nuclear talks kick off.

"We have just heard now ... that Secretary of State Kerry will also be here to address the council on Monday," council president Joachim Ruecker told reporters.

Pakistan's powerful spy chief has left on an official trip to the United States, the military said Wednesday, with possible peace talks between Afghanistan and the Afghan Taliban likely to be on the agenda.

It is Lieutenant General Rizwan Akhtar's first official visit to the U.S. since taking charge of the Inter-Services Intelligence (ISI) agency last year.