G7 foreign ministers met in Germany on Tuesday looking to build on recent progress on the Ukraine crisis and Iran's nuclear programme, host Frank-Walter Steinmeier said.

As the top diplomats of seven world economic powers gathered in the northern port city of Luebeck for two days of talks, Steinmeier said they would also seek fresh ideas for dealing with hotspots such as Yemen.

"As always with the G7 foreign ministers, we are addressing the decisive question of how we achieve peace in this world," he told reporters.

"How do we manage to at least diminish the danger of crisis situations and conflicts."

Steinmeier travelled to Luebeck fresh from four-way talks in Berlin with his counterparts from Russia, Ukraine and France to assess the shaky ceasefire in eastern Ukraine.

He admitted that the five-hour-long discussions in a lakeside villa had been "very contentious" but produced a "result that was quite encouraging".

This included a renewed commitment to the truce agreement signed in Minsk eight weeks ago despite a recent flare-up in fighting, and an expansion of its pledge for a withdrawal of heavy weapons from eastern Ukraine to include lighter artillery.

On a framework agreement reached with Iran on its nuclear programme, Steinmeier said the ministers would discuss what he called a "good foundation" for hammering out a final treaty by a June 30 deadline.

Steinmeier admitted that the international community was "still at the start of our efforts to calm the situation" in Yemen, where Shiite rebels launched a sweeping offensive that forced UN-backed President Abedrabbo Mansour Hadi to flee overseas.

"We will take the opportunity... to swap a few ideas about how we can at least begin to prevent the bloody conflict from continuing," he said.

The G7 is a grouping of leading developed economies -- Britain, Canada, France. Germany, Italy, Japan and the United States.

Formerly the G8, the grouping was reduced to seven members in 2014 after Russia's annexation of Crimea.

US Secretary of State John Kerry is only expected to arrive in Luebeck Wednesday as he was detained in Washington urging lawmakers not to interfere in the sensitive Iran nuclear talks.

Iranian Foreign Minister Mohammad Javad Zarif said Tuesday that Tehran and world powers would resume negotiations on April 21 aimed at reaching the final agreement.