UN special envoy Hans Grundberg started his first visit to Yemen's rebel-held capital Monday, following an April 2 ceasefire that the country's warring parties have accused each other of violating.

The Swedish diplomat is scheduled to meet Huthi rebel officials during his first Sanaa visit since taking office in September.

"He is looking forward to engaging with Ansar Allah (Huthi) leadership on implementing and strengthening the truce and discussing the way forward," Grundberg's office said in a tweet announcing his arrival.

Israeli forces launched a third day of operations Monday around the flashpoint West Bank city of Jenin following heavy gun battles in recent days and 20 arrests overnight, the army said.

Tensions have soared since a spree of attacks in Israel left 14 people dead in the past three weeks, with Prime Minister Naftali Bennett warning the Jewish state is now "on the offensive".

Four Palestinians were killed in separate incidents across the occupied territory Sunday, and militant groups in Jenin braced for more battles.

In a bombed-out building in northwest Syria, rescue workers who for years have braved Russia's war strategies film a tutorial video for Ukrainian volunteers crammed with tips gained from first-hand experience of treating casualties.

Using a dummy, members of Syria's "White Helmets" civil defence force demonstrate how to apply bandages and tourniquets in a clip shot in the rebel-held town of Ariha in Idlib province where Russian airstrikes are relatively routine.

Israeli forces Sunday raided the flashpoint West Bank district of Jenin, home of gunmen who launched two recent deadly attacks in Tel Aviv, as Prime Minister Naftali Bennett warned the Jewish state had "gone on the offensive".

The military operation entered its second day as Israel buried three civilian victims from last Thursday's shooting spree and Palestinian militant groups in Jenin warned they were mobilising fighters.

Iran's foreign minister said Sunday that Washington is "imposing new conditions" in the negotiations to restore the 2015 nuclear agreement.

"On the issue of lifting sanctions, they (the Americans) are interested in proposing and imposing new conditions outside the negotiations," state news agency IRNA quoted Hossein Amir-Abdollahian as saying.

"In the last two or three weeks, the American side has made excessive demands that contradict some paragraphs of the text," he added.

Garbage clogs the banks of Iraq's Tigris River in Baghdad but an army of young volunteers is cleaning it, a rare environmental project in the war-battered country.

With boots and gloves, they pick up soggy trash, water bottles, aluminium cans and muddy styrofoam boxes, part of a green activist campaign called the Cleanup Ambassadors.

"This is the first time this area has been cleaned since 2003," shouts a passer-by about the years of conflict since a US-led invasion toppled dictator Saddam Hussein.

The wheat fields of northern Yemen stretch into the distance but they aren't enough to nourish a country where millions go hungry.

Already teetering on the edge of famine, war-ravaged Yemen fears a shortage of the staple food ingredient because of a different war -- in Ukraine, which is one of the world's major suppliers of the grain.

In a bustling Sanaa bakery, Mohammed al-Jalal and his staff sell small loaves of bread to customers carrying them away in red plastic bags.

Former hostages taking the witness stand at the trial of their alleged Islamic State group captor have described their brutal treatment in chilling detail.

Eight former IS hostages have testified so far at the trial of El Shafee Elsheikh, accused of being a member of the notorious kidnap-and-murder cell known as the "Beatles."

But in a quirk of the case -- none of the former IS captives has been asked so far to formally identify their alleged captor in court.

A dust storm that has swept through much of Iraq has left dozens of people in hospital with respiratory problems, a health ministry spokesman said Saturday.

The storm erupted in the north of the country on Thursday, prompting the cancellation of flights serving Arbil, capital of the autonomous Kurdistan region.

As the storm swept south, it shrouded Baghdad and cities as far south as Nasiriyah in a ghostly orange.

In the capital, buildings and vehicles were covered in ochre-coloured dust, AFP journalists reported.

The Al-Hol camp for displaced people in Syria is a jihadist threat and should be dismantled, a senior Iraqi security official said on Saturday.

Al-Hol, in the Kurdish-controlled northeast, is Syria's largest camp for displaced people. It houses about 56,000 including displaced Syrians and Iraqi refugees, some of whom maintain links with the Islamic State group (IS).

About 10,000 are foreigners, including relatives of jihadists.