Ukrainian forces are holding back Russia's concerted summer push to break through defenses along parts of the front line, Ukraine's President Volodymyr Zelensky says.

"They are not advancing. It's very tough for our guys out there. And it's tough everywhere," Zelensky told reporters on Thursday, in comments embargoed till Friday. "It's also very hard for the Russians — and that's good for us."

The Kremlin said Friday that it was "obviously" unlikely Ukrainian President Volodymyr Zelensky and Vladimir Putin would meet within 30 days, after Kyiv suggested a leaders summit before the end of August.

"A high-level meeting can and must put a definitive end to the settlement ... Is it possible to go through such a complex process in 30 days? Well, that is obviously unlikely," Kremlin spokesman Dmitry Peskov told reporters including AFP.

Iran on Thursday reaffirmed its right to enrich uranium, saying it was "unshakable", on the eve of key talks with European powers threatening to reimpose sanctions.

"Especially after the recent war, it is important for them to understand that the Islamic Republic of Iran's position remains unshakable, and that our uranium enrichment will continue. We will not give up this right of the Iranian people," Foreign Minister Abbas Araghchi was quoted as saying by Tasnim news agency.

Tens of thousands of people sought refuge on Friday as border fighting between Thailand and Cambodia entered a second day, heightening fears of a broader conflict.

The U.N. Security Council is scheduled to hold an emergency meeting on the crisis later Friday in New York, while Malaysia, which chairs a regional bloc that includes both countries, called for an end to hostilities and offered to mediate.

Iranian and European diplomats met Friday in Istanbul to embark on the latest drive to unpick the deadlock over Tehran's nuclear program.

Representatives from Britain, France and Germany, known as the E3 nations, gathered at the Iranian consulate building for the first talks since Iran's 12-day war with Israel in June, which involved U.S. bombers striking nuclear-related facilities.

Aircraft from Lebanon, Jordan, Spain and Israel were on their way Thursday to help battle a huge wildfire in Cyprus that has claimed the lives of two people. Police were investigating reports that arsonists were to blame.

The flames have scorched more than 120 square kilometers (46 square miles) of forested hillsides in one of the worst such blazes in recent memory.

The United States on Wednesday announced the approval of $322 million in arms sales to bolster Ukraine's air defenses and its armored combat vehicles.

A delegation from the International Atomic Energy Agency will visit Iran within two to three weeks, an Iranian official said Wednesday, adding that the group will not have access to the country's nuclear sites.

The White House pulled out all the stops Wednesday to promote claims that Barack Obama headed a "treasonous conspiracy" against Donald Trump, seeking to redirect public attention from uproar over its handling of the Jeffrey Epstein affair.

Iranian forces warned a U.S. destroyer to stay out of waters claimed by Tehran, state television reported, an interaction a U.S. defense official said was "safe and professional" and did not affect the ship's mission.