The Ukraine standoff claimed the life of a Red Cross aid worker for the first time after heavy shelling hear the organization's office in the city of Donetsk.

"One of our colleagues was killed when a shell hit close to our office. We're deeply distressed by the loss," the International Committee of the Red Cross (ICRC) wrote on Twitter.

The victim was a Swiss citizen, the organization also reports.

ICRC currently has about 20 staff in Donetsk and all are now in safety, it said in a statement published on its website.

Ukraine's Foreign Minister Pavlo Klimkin blamed pro-Russian rebels for the incident, which comes despite a fragile truce both Kiev and militants insist they are observing.

Shelling has reportedly been renewed in some parts of Donetsk, UNIAN news agency informs.

At least 10 civilians could have been left dead and 40 wounded after one of the sides opened fire in the city on October 1.

The Organization for Security and Cooperation in Europe (OSCE) has called on both Ukrainian authorities and rebels to uphold the truce, immediately ending all hostilities.

EU officials have recently raised concerns about the ongoing clashes near the Donetsk airport.