Saudi Arabia has responded to calls for a ceasefire in its war on Yemen with a heavy bombing of the capital Sana'a with more than 30 airstrikes.

Yemen's al-Masirah TV said the airstrikes early Friday targeted al-Dulaimi Air Base in Sana'a and the surrounding areas as Saudi-backed troops launched new attacks further west in the country's main port city of Hudaydah.

Saudi Arabia and the UAE on Wednesday massed thousands of additional troops near the city which is a gateway to the capital, and the lifeline for imports and relief supplies into Yemen.

Witnesses in Hudaydah said fighting was heard in areas near the airport and the university, and Apache helicopters were spotted in the sky. Airstrikes were intensified on Thursday night on Houthi bases near the eastern entrance to the port city, they said.

Yemeni armed forces and allied Houthi fighters responded to the attacks with a newly-unveiled Badr P-1 missile launched at an enemy assembly in the Saudi Najran province.

The stepped-up attacks by Saudi Arabia came after calls for a ceasefire and the renewal of peace talks by the US and Britain which are key supporters of the kingdom in the war which has been going on since March 2015.

On Thursday, US Defense Secretary Jim Mattis and Secretary of State Mike Pompeo called on all sides in the war to agree to a truce within the next 30 days.

The Houthis have expressed readiness for peace talks but strongly opposed the US proposal for mediation in the conflict, holding Washington responsible for the aggression against Yemen.

The Houthis believe that the only solution to the crisis lies in intra-Yemeni talks and non-interference by foreign parties, Houthi Political Council member Mohammed al-Bakhiiti said on Thursday.

Saudi Arabia has been waging the war against Yemen with the aim of reinstating former Yemeni president Abd Rabbuh Mansour Hadi.

The war, coupled with a Saudi naval blockade, has destroyed Yemen's infrastructure and led to famine as well as a cholera outbreak in the import-dependent state.

Last month, the Legal Center for Rights and Developments in Yemen said more than 15,000 civilians have died as a result of the conflict so far.

Patrick Cockburn, an award-winning columnist for the British daily The Independent, said this week the number of casualties remains unreported due to a media blackout, putting the death toll at around 56,000.