German Foreign Minister Frank-Walter Steinmeier has demanded an end to systematic starvation practices in Syria and called for an unhindered humanitarian access to besieged regions in the war-torn country.

"Situations like Madaya, where thousands of people have been besieged and systematically starved can no longer be acceptable," Steinmeier said Wednesday, after his meeting with the Syrian opposition's negotiations coordinator, Riyad Farid Hijab.

Steinmeier said parties to the conflict should take steps that would ease the suffering of the civilian population.

Talks between opposition and Syrian regime are scheduled for Jan. 25 in Geneva.

"We have urged from the very beginning that the issue of unhindered humanitarian access should be on the agenda during talks in Vienna and New York. Everybody has agreed on that, now it is time for the implementation," Steinmeier said.

The southern Syrian town of Madaya was blockaded by the Syrian regime and Hezbollah militants for close to 200 days.

On Monday, a humanitarian convoy reached the town with life-saving health and food supplies for 42,000 desperate residents after reports of people starving to death.

Talks for a political settlement

Steinmeier praised unity achieved among Syrian opposition groups ahead of talks in Geneva, and expressed hope for progress towards agreement on a transition process.

"We will support efforts of UN special envoy [Staffan] de Mistura with all our strength, we will give our political and financial support, and also provide personnel, our best experts," he said.

Steinmeier called on Iran and Saudi Arabia to de-escalate recent tensions and not ruin the progress achieved in the last couple of months towards a political solution to the Syrian conflict.

"For that, today I have talked with my Saudi counterpart on the phone," Steinmeier said.

"And this will be the special focus of my contacts and travel in the region in the near future," he added.

The Syria conflict, which will enter its sixth year in March, has left more than 250,000 people dead and turned the country into the world's largest source of refugees and displaced persons, according to the UN.

Approximately 4.5 million people live in hard-to-reach areas across the country, with nearly 400,000 of them in 15 besieged locations with little or no access to basic supplies or assistance.