Ukraine 'on Full Combat Alert' against Possible Russia Invasion as Putin, Cameron Urge 'Peaceful' Solution

Pro-Russian insurgents Wednesday lifted an armed siege of a regional police headquarters in the eastern Ukrainian city of Lugansk after the chief officer agreed to resign, as Kiev said its army is on "full combat alert" against a possible Russian invasion.

A police spokeswoman said the officers inside had refused to give up their weapons to a crowd of some 1,000 pro-Moscow militants led by 30 or so armed men carrying Kalashnikov assault rifles and grenade-launchers, who had tried to storm the building overnight.

"The chief inspector has resigned. We are awaiting the appointment of his successor. In the meantime, the Lugansk police is functioning normally -- well, as normal as could be expected under the circumstances," the spokeswoman said.

The police HQ was the scene of a tense stand-off late Tuesday between the protesters and the police who had barricaded inside the building in the city of 465,000 people. 

Rebels already hold the SBU security services building and the regional administration building.

The protesters tried to smash down the metal door of the headquarters and the police replied with volleys of tear gas and stun grenades.

Late Tuesday, some 30 or so visibly scared police conscripts were led out of the building through a hostile crowd and onto waiting buses. But their higher-paid professional superiors remained inside.

The Western-backed authorities in Kiev have voiced exasperation at what the interim president has called the "inaction" and "treachery" of the police services who have at times stood by while violence raged.

Many police officers in the east -- who receive monthly pay of just $200 -- have done little to stop the rebels taking public buildings. In some cases, they appeared to share the pro-Russian sympathies of the militants they were ordered to square off against.

Kiev has urged civilian volunteers in the east to join territorial brigades to help back the police, but so far there was no sign of that happening.

Earlier on Wednesday, Ukraine's acting President Oleksandr Turchynov said the country's military is "on full combat alert" against a possible invasion by Russian troops massed on the border.

"Our armed forces are on full combat alert," he told a ministerial meeting in Kiev.

"The threat of Russia starting a war against mainland Ukraine is real."

His comments came as Ukraine's army and police appeared to be making little progress in a high-profile operation to stop pro-Russian rebels expanding their grip over towns in the restive east.

Turchynov several weeks ago also announced Ukraine's defense forces had been put on high alert, but there was no visible sign of any increased readiness.

Russia deployed an estimated 40,000 troops to its shared border with Ukraine in March. Moscow initially said they were mobilized for exercises but last week said they were ready to respond to Kiev's military offensive against pro-Kremlin rebels.

Russian President Vladimir Putin asserts he has a "right" to send his forces into Ukraine but has not yet done so.

Kiev and Washington, however, say Russian special forces are already active in east Ukraine, leading an insurgency that has overrun 14 towns and cities.

Turchynov told the cabinet meeting that "our number one task is to prevent terrorism spreading from the Donetsk and Lugansk regions to other Ukrainian regions."

He underlined moves announced a day earlier to set up armed civilian "territorial volunteer militia" units to help beleaguered police and troops in the restive east.

Later on Wednesday, Putin and British Prime Minister David Cameron agreed in a phone conversation that an end to the crisis in Ukraine can only be reached through peaceful means, the Kremlin said in a statement.

"The leaders of Russia and the United Kingdom agreed that the end of the serious political confrontation can only be reached through peaceful means. They agreed to continue bilateral exchange at several levels," the statement said.

The Kremlin said the phone call was initiated by Cameron and that Putin took the opportunity to underline the "fundamental importance of a swift and unconditional implementation of the April 17 Geneva accord."

That deal between Russia, Ukraine, the EU and United States was intended to ease tensions in Ukraine with a requirement that all armed groups lay down their arms and for a cessation of violence.