* Eastern Ukrainian region builds trench on Russian border
* Measures to be taken against violent protesters - governor
* Russia says reserves right to "protect" Russian speakers
By Lina Kushch
DONETSK, Ukraine, March 17 (Reuters) - Ukraine's easterly Donetsk region, dominated by Russian-speakers and buffeted by rallies by pro-Russian activists, has built a defensive trench complete with concrete barriers along its long border with Russia, its governor said on Monday.
Sergei Taruta also said measures would be taken to restore order in the region in the aftermath of Russia's takeover of Crimea after pro-Russian demonstrators overwhelmed police and stormed public buildings.
Russian President Vladimir Putin says he reserves the right, after the takeover of Crimea, to protect eastern Ukraine's Russian-speaking majority from what Moscow says are right-wing allies of the pro-Western government in Kiev. Ukraine's defence minister says 60,000 Russian troops are massed on the border.
Taruta, appointed by the central government like all regional governors, said the aim of the trench project was to protect the 150 km (90 miles) of Donetsk region's border with Russia, particularly between established crossing points.
The trench, he said, was 4 metres (12 ft 6 in) wide, 2.5 metres deep and backed up by a dike 2 metres high.
"We have done this on our own and dug a trench practically the entire length of the border. In particularly dangerous places, concrete blocks standing on four legs have been put in place," Taruta told a news conference.
"Our border is not a castle. But it is equipped so that vehicles cannot cross it in either direction. This is not based on one or another scenario, but rather intended to maintain a solid border."
Pictures posted on various Internet sites showed servicemen on patrol in the trench, with the large dike looming above them.
Donetsk is the home region of ousted president Viktor Yanukovich, removed last month after three months of sometimes violent protests against his decision, under Russian pressure, to abandon an agreement on close links with the European Union.
The government that came to power after his flight from Ukraine is firmly pro-Western. Moscow says it is linked to extreme right-wing groups who played a major role in the protests that led to Yanukovich's overthrow.
One demonstrator died in Donetsk last week after clashes between activists at rival rallies, one backing Russia and its takeover of Ukraine's Crimea region, the other Ukraine's drive to move closer to western Europe. Two activists died in unrest in Kharkiv, in northeastern Ukraine.
Taruta said measures would be taken to ensure that pro-Russian protesters who have been staging rallies for weeks in Donestsk would no longer force their way into public buildings.
On Sunday, a group of several thousand smashed their way into the local prosecutor's office to press demands for the release of a man who briefly proclaimed himself governor this month.
"This was a pre-planned action and they were trying to provoke us. We therefore did not try to stop them storming the building," he said.
"But as of tomorrow, the picture will be entirely different. The law will be respected and the security forces will be present. There will be changes in personnel."
He said the local police force had the numbers and the means to deal with the activists.
On Monday, several hundred pro-Russian activists massed in front of the regional administration building and were invited by regional council officials to attend a forthcoming meeting.
The protesters then dispersed peacefully, saying they were satisfied their demands would be examined. (Writing by Ron Popeski; Editing by Alison Williams)