Nato foreign ministers are due to discuss ways to help Ukraine and reassure allies in Eastern Europe, at a meeting in Brussels.

It is the first time ministers from the 28 member states have convened since Russia's takeover of Crimea caused a diplomatic crisis.

Nato has bolstered annual air drills being held over Baltic countries later.

On Monday, Russia ordered a partial withdrawal of its troops from the border with Ukraine.

Russian President Vladimir Putin told German Chancellor Angela Merkel he had ordered the move, according to the German government.

Thousands of Russian soldiers are still said to be deployed along the eastern border of Ukraine.

Meanwhile, Russian energy firm Gazprom is increasing the price it charges Ukraine for gas from Tuesday.

Gazprom's chief executive Alexei Miller said last month that Kiev had failed to pay its bills, believed to be more than $1.5bn (£900m).

Tensions between Russia and the West rose after the overthrow of pro-Kremlin Ukrainian President Viktor Yanukovych in February, following months of street protests.

Russia's subsequent decision to annex Crimea triggered a crisis in relations.

The US and EU have imposed sanctions on members of President Putin's inner circle and other officials. Russia has retaliated with its own sanctions on US politicians.

Rattled nerves

Nato foreign ministers are expected to discuss the formal suspension of co-operation with Moscow at the Brussels meeting.

In a statement, the alliance said ministers would speak to Ukrainian Foreign Minister Andriy Deshchytsia about ways to support Ukraine with its defence reforms.

They are also expected to look at options including situating permanent military bases in the Baltic states to reassure members in Eastern Europe.

Russia's actions in Ukraine have rattled nerves in Estonia, Latvia and Lithuania, which were part of the Soviet Union during the Cold War.

Nato jets will take part in air patrols in the region later in a routine exercise that analysts say has taken on added significance due to the crisis.

Several Nato countries, including the UK, US and France, have offered additional warplanes.

'Crude violation'

Earlier, Ukraine condemned a visit to Crimea by Russia's Prime Minister Dmitry Medvedev and a delegation of government ministers.

A foreign ministry spokesman in Kiev said the highest-level trip to the Black Sea peninsula by officials from Moscow since its annexation by Russia was a "crude violation" of international rules.

Crimeans voted to leave Ukraine for Russia on 16 March, in a referendum condemned as illegal by the UN General Assembly.

Mr Medvedev announced that he would make Crimea a special economic zone, with tax breaks and reduced bureaucracy to attract investors.

He also vowed to quickly boost salaries and pensions, and to improve education, healthcare and local infrastructure.

Source: BBC