The official death toll for Burma's cyclone disaster has jumped to almost 78,000 people, with nearly 56,000 missing, according to state TV.

The numbers are nearly double those released on Thursday, raising fears the final human toll may be enormous.

The Red Cross is seeking more than $50m (£26m) in aid to help survivors of the storm which struck on 2-3 May.

Foreign aid agencies are frustrated at the slow progress of aid to areas worst hit, especially in the Irrawaddy Delta.

A BBC reporter in the delta this week saw little sign of official help and foreign aid workers have been barred from the area.

Heavy rain has been lashing the region, compounding the misery of survivors of Cyclone Nargis.

The UN Humanitarian Co-ordinator, John Holmes, is due to visit Rangoon, Burma's main city, on Sunday in a bid to persuade the military government to grant more access to UN relief workers and expand its aid effort.

Earlier, the EU's top aid official, Louis Michel, was denied permission to visit the delta region. He said he was given no explanation why disaster emergency experts were being refused visas.

However, Burma - also known as Myanmar - has promised to take foreign diplomats on a tour of the region this weekend.

'Beggars for miles'

Previously, Burma was giving a toll of 43,000 dead and 28,000 missing while the Red Cross and United Nations had estimated a death toll above 100,000.

The Burmese blamed the sudden increase in the death toll on difficulties they have had confirming what has happened to people in the worst-affected areas.

The difficulty in getting accurate figures is inevitable bearing in mind the scarce resources there are on the ground to assess the needs of those affected by this disaster, the BBC's Chris Hogg reports from Bangkok.

The lack of solid information makes the task of planning how to help them even harder, he adds.

It is not clear how much access the foreign diplomats will have to areas outside the official tour route.

On a trip to the Delta this week, the BBC's Natalia Antelava saw muddy river banks lined with white, swollen bodies, and found survivors with barely enough rice to live on.

A Reuters team travelling to Kunyangon, around 100km (60 miles) south-west of Rangoon, found rows of beggars stretching for miles on either side of a road.

Men, women and children stood in the mud and rain, hands clasped together in supplication at the occasional passing aid vehicle.

One woman, in her 60s, said she had only survived the storm by climbing a tree.

'Time is life'

Many relief workers are awaiting visas and most of those who have been allowed into the country remain confined to Rangoon.

Speaking in Bangkok after his visit to Burma, the EU's Louis Michel said the world needed to impress upon Burma's rulers the urgency of survivors' needs.

"Time is life," he told AFP news agency.

"Every possible pressure - all rhetorical and diplomatic means - must be used to get them to understand that they must help us help them."

The UN's John Holmes had his visa for Burma approved on Thursday night.

At this stage it is not clear who he will be able to talk too given that Burma's leader, Thein Sein, has refused even to pick up the phone to talk to Mr Holmes's boss, the UN Secretary General Ban Ki-Moon, our correspondent notes.

In the last few days, Burma has agreed to allow a few experts from neighbouring countries in to help, our correspondent notes.

It may not be as many as the international community thinks are needed, he says, but UN officials believe this is an opportunity to show the military government that aid-workers' motives are humanitarian, not political.

Water alert

According to the Red Cross, aid agencies have been able to reach only around 20% to 30% of cyclone victims and hundreds of thousands of people are at risk of diseases such as dysentery because of lack of clean water.

"If clean water isn't available, it's going to be the biggest killer in the post-disaster environment," Thomas Gurtner told the Associated Press news agency.

Speaking in Geneva, Mr Gurtner predicted "further destitution among an already very hard-hit population", noting that the harvest had already been lost.

The Association of South East Asian Nations (Asean) is due to hold a high-level meeting in the coming days that is expected to lay the framework for a broader aid donors conference.

Burma's military leadership has warned that those who hoard or sell aid on the black market will be prosecuted, amid international reports of misuse of some aid shipments.