MOSCOW (AP) - President Vladimir Putin says that starting next month Russia will deliver gas to Ukraine only if it pays in advance.

MOSCOW (AP) President Vladimir Putin says that starting next month Russia will deliver gas to Ukraine only if it pays in advance.

Putin first warned that Russia to do so in April, in a letter to European leaders whose nations are customers of Russian state-controlled Gazprom natural gas giant. He said Moscow would have to demand advance payment if Ukraine failed to start settling its mounting gas debt.

In the second letter released by the Kremlin Thursday, Putin said that a meeting involving Russian, Ukrainian and the European Union officials has failed to settle the issue. Putin said that Ukraine's gas debt to Russia has kept rising and has reached $3.5 billion.