The UN refugee agency expects at least 1.4 million refugees to flee to Europe across the Mediterranean this year and next, according to a document seen by Reuters on Thursday, a sharp rise from initial estimates of 850,000.

"UNHCR is planning for up to 700,000 people seeking safety and international protection in Europe in 2015," reads the document, a revision to the agency's existing appeal for funds.

"... It is possible that there could be even greater numbers of arrivals in 2016, however, planning is based for the moment on similar figures to 2015."

UNHCR launched the appeal on Sept. 8 with preliminary plans for 400,000 refugee arrivals in 2015 and 450,000 in 2016. But the 2015 figure was surpassed within days of its publication, and by Sept. 28, 520,957 had arrived.

Broadened appeal

The revised appeal totals $128 million, a sharp increase from the initial appeal for $30.5 million, and UNHCR asked donors to allow their funds to be allocated flexibly because of the "very volatile operational context".

The appeal is also broadened to include transit countries in the Middle East and North Africa, to enable refugees to get help from UNHCR at an earlier stage of their journey.

Although the vast majority of recent arrivals have travelled from Turkey through Greece, Macedonia and Serbia, possible alternative routes mapped out by UNHCR include the sea route from Turkey to Italy, from Greece through Albania to Montenegro or Italy, and from Montenegro by boat to Croatia.

Most are fleeing the Syrian civil war, with many others seeking to escape conflict or poverty in Iraq, Afghanistan, Africa or elsewhere.

The revised appeal covers plans to scale up the emergency response to protect and give aid to the higher numbers of refugees, but a further revision may be published later in the year to reflect additional needs for European contingency planning, the document said.