The UN refugee agency has sharply revised up its previous estimates for the number of refugees who are expected to arrive in Europe during 2015 and 2016.

“UNHCR's response is now based on the assumption that up to 700,000 people will seek safety and international protection in Europe in 2015, and possibly even higher numbers in 2016,” the Office of United Nations High Commissioner for Refugees (UNHCR) said on Thursday, issuing a revised funding appeal.

The new figure shows a sharp rise from the agency's early September estimate of 850,000 for both this year and the next.

"...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,” the agency added.

UNHCR spokesman Adrian Edwards said the estimate is specifically related to the refugees taking the Mediterranean route to seek shelter in Europe.

The new funding appeal comes as the European Union is struggling to find an integrated mechanism to cope with the increasing number of people heading to European borders. Interior ministers of the 28-nation bloc agreed on September 22 on a plan to relocate 120,000 refugees, despite fierce opposition from some eastern European governments opposing mandatory quotas for accommodating the refugees.

On Thursday, officials in the European Commission, the powerful executive wing of the EU, threatened to take action against Hungary over laws it has introduced to stem the flow of refugees through its territory.