The United States denounced the "brutality" of Islamic militants Thursday as it unveiled its annual assessment of the state of human rights around the world.

"No development has been more disturbing than the rise of groups such as Daesh," Secretary of State John Kerry said, referring to the Islamic State group, as he unveiled the report at the State Department.

Down-to-the-wire talks in Vienna this week will decide whether the United States can reach a landmark nuclear deal with Iran, but a fierce lobbying battle in Washington may decide if it survives.

For the last two years, those for and against an agreement to curb Iran's nuclear program have traded newspaper opinion pieces, rolled out dueling advocacy campaigns and lobbied "influencers" on the think tank circuit.

Iran held a joint funeral on Thursday for three nationals killed fighting the Islamic State group alongside forces of its close ally Syria, state media reported.

The memorial service for the three Iranians, all from Tehran, was attended by around 2,000 people, the official IRNA news agency reported.

Three Saudi soldiers and an Emirati have been killed on Saudi Arabia's border with Yemen, where Riyadh is a leading a bombing campaign against Iran-backed rebels, state media said Thursday.

Two Saudi troops were killed at sunset Wednesday when a rocket landed in the Jizan region, the Saudi-led coalition said in a statement carried by the SPA state news agency.

Iranian Foreign Minister Mohammad Javad Zarif will travel to Vienna on Saturday to join a final push for a comprehensive nuclear agreement with major powers, state media reported.

"On Saturday morning, he will join his deputies who are at the talks drafting the text of a comprehensive agreement," the official IRNA news agency reported on Thursday.

President Barack Obama urged Beijing to take "concrete steps" to ease tensions over cyber hacking and its wide-ranging maritime claims, as the United States and China ended three days of candid talks.

American officials have voiced deep concerns about both issues at the annual strategic and economic dialogue aimed at setting guidelines to steer future ties between the world's two leading economies.

A controversial law on safeguarding Iran's nuclear rights was found to be constitutional Wednesday despite opposition from the government, which considers it an obstacle in negotiations with world powers.

"The bill obliging the government to preserve nuclear rights and achievements... was not considered to be contradictory to religion nor the constitution and was approved by a majority of votes of Guardian Council members," council spokesman Nejatollah Ebrahimian said, quoted by Fars news agency.

Iran's supreme leader Ayatollah Ali Khamenei restated his country's red lines for a nuclear deal Tuesday, during a meeting with President Hassan Rouhani and top officials in Tehran.

Banking and other economic sanctions imposed by the U.N. and the United States must be lifted "immediately" if a nuclear deal is signed, he said, according to a transcript posted on his official website.

Iranian Foreign Minister Mohamed Javad Zarif will meet several of his EU counterparts on Monday, a European source said, ahead of a June 30 deadline for an international accord on Tehran's nuclear program.

"This will be a political meeting as part of the current negotiations, ahead of the final round," the source said Sunday, adding that the EU ministers attending would be Britain's Philip Hammond, France's Laurent Fabius and Germany's Frank-Walter Steinmeier.

French Foreign Minister Laurent Fabius said Sunday any nuclear deal with Iran must be verifiable as he prepared to meet his Iranian counterpart with a deadline looming for an agreement.

"We think that we must be extremely firm and that, if an agreement is to be reached, that agreement must be robust," Fabius told journalists at a joint news conference with Israeli Prime Minister Benjamin Netanyahu, who strongly opposes the deal currently on the table.