Both sides in the Ukraine conflict have cast doubt on a newly called ceasefire, following the downing of a military helicopter on Tuesday.

Pro-Russia separatist leader Alexander Borodai said that in his view there had "been no ceasefire".

Ukraine's President Petro Poroshenko warned he might end the truce due to "constant violation by rebels".

Nato chief Anders Fogh Rasmussen has accused Russia of failing to "respect its international commitments".

In a statement, he said Moscow was "using a new different type of warfare against Ukraine" and he promised a "package of long-term support measures for Ukraine, including the creation of new trust funds".

Russia denies claims by Ukraine and the West that it is encouraging and arming the separatists.

Insurgents had agreed on Monday to observe a ceasefire, proposed by the Ukrainian government, until Friday, but on Tuesday the Ukrainian military announced that separatists had shot down an Mi-8 helicopter outside the rebel-held city of Sloviansk, killing all nine people on board.

Mr Poroshenko's office said gunmen had attacked government forces on 35 occasions since he ordered his troops to hold their fire.

The ceasefire is part of Ukraine's plan to end two months of fighting between government troops and pro-Russian insurgents who control key buildings in towns and cities across the east.

More than 420 people have been killed in the region since mid-April, the UN estimates.

Source: BBC