UN battles to keep Yemen's aid lifeline open as Saudi coalition starts attack

"We are in constant contact with all the parties involved to negotiate arrangements for Hodeida that would address political, humanitarian, security concerns of all concerned parties," said Martin Griffiths in a statement.

The attack on Houthi-controlled Hodeida comes despite warnings from the UN and NGOs of a humanitarian disaster, exacerbating the already dire situation in Yemen where millions are on the brink of famine.

The Red Sea port is an access point for 70 percent of Yemen's imports, including vital aid supplies for civilians in the conflict-wracked country.

The UN warned on Monday that 250,000 residents could die if the city is put under siege.

Aid groups, which have pulled staff from the town over the detoriorating security situation, have warned of catastrophic consequences.

Save the Children on Wednesday said 300,000 children were in the line of fire.

In a statement it said it was "extremely concerned" that the port in Hodeida will be closed and "despite repeated warnings of the devastating impact this will have, a famine is becoming a real possibility, with hundreds of thousands of lives at risk".

Oxfam's Yemen chief, Muhsin Siddiquey, said: "An attack on Hodeida will bring death, destruction and push vital resources like food, fuel and medicine even further out of reach."

UN envoy Griffiths was in Amman following an intense round of shuttle diplomacy this week with Yemen's Houthi rebels, who control the port, Saudi Arabia and the United Arab Emirates, whose forces are backing the Hodeida offensive.

Yemen's exiled government said its forces and allied Saudi-led troops launched their assault only after "exhausting all peaceful and political means".

The statement on the government-controlled SABA news agency early Wednesday morning called the battle "a milestone in our struggle to get Yemen back from the militias".

The attack on Hodeida threatens to derail efforts to secure a political solution to the three-year war in Yemen, which has killed more than 10,000 people.

But Griffiths, who is due to brief the UN Security Council on Monday on a draft peace plan, remained committed to the endeavour.

"The United Nations is determined to move ahead with the political process despite the recent developments," he said.

Agencies contributed to this report.