MINSK (Reuters) – Belarus on Sunday signalled a growing rift with ally Russia, saying President Alexander Lukashenko would not attend a security summit in Moscow in protest at a Russian ban on dairy imports from Belarus.

Ties between former Soviet republics Russia and Belarus have been strained since 2007, with Minsk upset at steadily rising prices for Russian gas and Moscow angered by Lukashenko's growing overtures to the West.

Lukashenko had been due to take part in a summit of the Collective Security Treaty Organisation (CSTO), which groups Russia, Belarus, Armenia and four Central Asian states: Kazakhstan, Uzbekistan, Tajikistan and Kyrgyzstan.

But he pulled out after Moscow banned one of Belarus's key exports, dairy products. Russia said this was imposed on health grounds but Moscow has often used trade bans to put political pressure on neighbouring states.

"In the current situation, Belarus … is forced to cancel its participation in the CSTO meeting in Moscow on June 14," Belarus's Foreign Ministry said in a statement.

It was not feasible to take decisions about security unless there was a halt to actions which undermined the economic security of CSTO partners, the statement said. "We believe it would be a mockery of common sense against the background of 'trade wars' waged by some CSTO members against others."

Russian Foreign Minister Sergei Lavrov chided Minsk for linking what he said were economic problems to issues of military and political security.

"Honestly, we cannot comprehend the motives behind the Belarussia side's decision not to take part in the CSTO events in Moscow today," Lavrov told the Interfax news agency.

Russia froze a $500 million loan to Belarus at the end of May, prompting an angry outburst by Lukashenko. He said Moscow refused the money because he turned down Kremlin demands to recognise the breakaway Georgian regions of Abkhazia and South Ossetia as independent states.

On June 6, Russia banned imports of dairy products from Belarus, cutting off a major source of exports for the indebted and struggling state, which still runs a largely Soviet-style command economy.

Lukashenko hit back by cancelling participation in Sunday's CSTO summit. The CSTO controls a key land route from Europe to Afghanistan and is sometimes billed as a counterweight to NATO.

It had been due to decide on Sunday on the creation of a rapid reaction force to fight common security challenges such as drug trafficking from Afghanistan and international terrorism.

"Our country will sign a package of documents on the rapid reaction force only once security within the CSTO has been restored in all its entirety," Belarus's Foreign Ministry said.

Slav neighbours Russia and Belarus have pledged to build a "union state" and have declared a passport and customs union, but progress towards political union has long been stalled and the latest moves have reversed progress in this area.

On Saturday, Lukashenko asked his ministers to look into the re-introduction of controls on the border with Russia.

Lukashenko has long been accused by the West of repressing dissent, muzzling the media and rigging elections.

But as relations with Moscow soured, he has tried to improve relations with the West by releasing dissidents from jail and promising to consider other political reforms.

Russia, the world's No.2 oil exporter and a holder of the third largest gold and forex reserves, has been trying to use the economic crisis to tighten its grip on less wealthy neighbours, largely dependent on trade with Russia.

(Writing by Dmitry Solovyov; Editing by Louise Ireland)