A Swiss man of Syrian Christian origin who battled the Islamic State group faces charges after returning home, raising the issue of how Europe handles citizens fighting IS.

European governments already face the headache of dealing with citizens who have gone to Syria to join the ultra-violent Islamist IS group. But volunteers in units fighting against IS pose a new problem.

Poland on Tuesday criticized a Swiss company's sale of high-tech camouflage netting to Russia despite Western sanctions over its role in the Ukraine conflict.

"It must be condemned... supplying this kind of equipment facilitates the aggression of the Russian military," Foreign Minister Grzegorz Schetyna told PAP news agency of the 85 million euros ($91 million sale).

Top diplomats from Iran and the U.S. began a new round of marathon talks on a nuclear deal late Monday, as Israeli leader Benjamin Netanyahu warned the emerging accord could threaten his country's survival.

U.S. Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif met in a Swiss lakeside hotel for a series of sessions which are scheduled to stretch into Wednesday afternoon.

The death toll from an avalanche that swept away a group of Italian skiers in the Swiss Alps has risen to four after a man died from his injuries, police said Sunday.

The man was part of the group hit by an avalanche on Saturday while in an area of the Swiss Alps known as "Death Valley."

Two trains slammed into each other near the Swiss city of Zurich early Friday, tipping over carriages and injuring at least six people, police said.

The driver of one of the trains was in serious condition after the crash, which saw ambulances, fire and rescue services rush to the scene as a rescue helicopter hovered above.

The Venezuelan government's bank accounts at the Swiss division of HSBC, which were revealed in the "SwissLeaks" scandal, are "totally transparent," said the South American country's economy minister.

Venezuela ranked third among the countries with the largest dollar amounts in the leaked Swiss files, behind Switzerland and Britain, journalists with access to the secret documents said at the weekend.

A 19-year-old American student who disappeared over the weekend while skiing in the Swiss Alps was rescued Tuesday, alive but suffering from hypothermia, police said Tuesday.

After searching for more than 48 hours, rescuers finally found the U.S. teen, who went missing while skiing off-piste Sunday near the Diablerets resort in southern Switzerland, police in the canton of Vaud said in a statement.

Another person has died after being overcome by an avalanche in the Swiss Alps while skiing off-piste, police said Sunday, bringing the death toll in such accidents to 10 in the past four days.

The woman, who died overnight in hospital, was part of a group of nine skiers hit by an avalanche on Saturday afternoon on the Piz Vilan mountain where they were skiing at an altitude of some 2,200 meters (7,200 feet).

Iranian and U.S. diplomats resumed talks in Switzerland on Friday, as the pace intensifies towards a complex deal on Tehran's nuclear program.

Two days of meetings between Iran's deputy foreign minister Abbas Araghchi and top U.S. negotiator Wendy Sherman began Friday morning in Zurich, a U.S. spokesman told AFP.

Diplomats from Iran and the U.S. are to meet again in Switzerland this week as the pace intensifies for a nuclear deal with Tehran, U.S. officials said Wednesday.

Top U.S. negotiator Wendy Sherman will travel to Zurich to meet with Iranian officials on Friday and Saturday, less than a week after leading face-to-face negotiations in Geneva, the State Department announced.