United Nations Secretary-General Antonio Guterres on Tuesday demanded Yemen's Houthi rebels release dozens of aid workers, including UN staff, a year after their arrest.

The United States has begun reducing its military presence in Syria with a view to eventually closing all but one of its bases there, the U.S. envoy for the country has said in an interview.

Moscow will only agree to a full ceasefire if Ukrainian troops pull back from the four regions that Russia partially controls, according to a copy of a negotiating document published by the state news agencies on Monday.

The memorandum was handed over to Ukraine during the second round of talks in Istanbul, and confirmed Russia's maximalist claims to the four partly occupied Ukrainian regions of Donetsk, Lugansk, Zaporizhzhia and Kherson.

U.S. President Donald Trump is open to an invitation by his Turkish counterpart to hold three-way peace talks in Turkey with the Russian and Ukrainian leaders, the White House said Monday.

"The president has said he's open to it if it comes to that, but he wants both of these leaders and both sides to come to the table together," Press Secretary Karoline Leavitt said when asked about Turkish President Recep Tayyip Erdogan's proposal.

The Israeli army said on Tuesday that three of its soldiers were killed in northern Gaza.

The latest deaths bring to 424 the number of Israeli troops killed in the Palestinian territory since the start of the conflict.

On Beirut's chaotic, car-choked streets, Lebanese student Fatima Fakih rides a shiny purple bus to university, one of a fleet rolled out by authorities to revive public transport in a country struggling to deliver basic services.

The 19-year-old says the spacious public buses are "safer, better and more comfortable", than the informal network of private buses and minivans that have long substituted for mass transport.

The UK has registered its warmest spring on record and its driest "in more than 50 years", its official weather service said on Monday.

Provisional temperatures averaged averaged 9.51 degrees Celsius (49.1 degrees Fahrenheit) from March to May, just above the previous spring record of 9.37 degrees, which was set only last year, the Met Office said.

Iranian Foreign Minister Abbas Araghchi said on Monday that a nuclear deal would not be possible if the goal is to "deprive Iran of its peaceful nuclear activities".

"If the goal of the negotiations is to gain reassurance and confidence that Iran is not seeking nuclear weapons, then in my view, reaching an agreement is possible," he said in a joint press conference with Egyptian foreign minister Badr Abdelatty. "But if the goal is to deprive Iran of its peaceful activities, then certainly no agreement will be reached," he continued.

Gaza's civil defense agency said an Israeli strike on a home in the northern town of Jabalia killed 14 people on Monday.

"The number of martyrs from the targeting of the Al-Bursh family home has risen to 14, including six children and three women, in addition to more than 20 missing individuals still under the rubble," agency spokesman Mahmud Bassal told AFP.

U.N. Secretary-General Antonio Guterres called on Monday for an independent investigation into the deaths of at least 31 Palestinians near a U.S.-backed aid distribution site in Gaza, after rescuers blamed the deaths on Israeli gunfire.

"I am appalled by the reports of Palestinians killed and injured while seeking aid in Gaza yesterday. It is unacceptable that Palestinians are risking their lives for food," Guterres said in a statement. "I call for an immediate and independent investigation into these events and for perpetrators to be held accountable."