US Secretary of State Antony Blinken on Monday urged the Iran-backed Huthi rebels to halt their offensive in northern Yemen, as he announced $191 million in aid at a donor conference.

The Huthis last month resumed a push to capture Marib city, which lies close to some of Yemen's richest oil fields.

Blinken pledged the humanitarian assistance at a virtual donors' conference co-hosted by Sweden and Switzerland, which aims to raise $3.85 billion to prevent large-scale famine engulfing the country.

But he warned that the suffering would not stop until a political solution is found between the Huthis and the internationally recognised government which is backed by a Saudi-led coalition.

"Aid alone will not end the conflict. We can only end the humanitarian crisis in Yemen by ending the war... so the United States is reinvigorating our diplomatic efforts to end the war," he said. 

Blinken called on the Huthis to cease the cross-border attacks and military offensives that he said had prolonged the war.

Saudi Arabia has repeatedly been targeted by missile attacks claimed by the Yemeni rebels. 

"The necessary first step is to stop their offensive against Marib, a city where a million internally displaced people live, and to join the Saudis and the government in Yemen in making constructive moves towards peace," he said.

The battle for Marib has threatened camps for internally displaced people who have fled there during the six-year war.

Around 140 sites have sprung up in the region to provide basic shelter for the displaced, who number up to two million, according to Yemen's government.

The United Nations has warned of a looming humanitarian disaster if the fight for Marib continues, saying it has put "millions of civilians at risk".