* Baghdad, Kurdish tensions high after military build-up
* In past, Kurdish, Iraqi forces pulled back before clashes
* U.S. officials seeking to ease frictions, sources say
Iraq's central government and the country's autonomous Kurdistan region have each sent troops to reinforce their internal border as tension builds between them in a feud over land and oil.
The second military build-up this year illustrates how far relations between Baghdad's Arab-led central government and ethnic Kurds have deteriorated in a rift that is testing Iraq's federal unity nearly a year after American troops left.
U.S. officials were in contact on Tuesday with Iraqi and Kurdish leaders to ease tensions and the area, Tuz Khurmato, 170 km (105 miles) north of Baghdad, appeared stable for now, according to Iraqi security and Kurdish sources.
Washington has intervened in past stand-offs when Iraqi army and Kurdish troops known as Peshmerga came close to confrontation only to pull back at the last moment after testing each other's nerves without any real appetite for a fight.
A spokesman for the commander in chief of the Iraqi armed forces described the deployment as a "precautionary measure" and told Reuters the troops were under instruction to exercise the utmost self-restraint to avoid further escalation.
Earlier he warned Kurdish troops not to change positions or come close to government troops.
Tensions have been steadily building this week over the formation of a new command centre for Iraqi forces to operate in an area over which both Baghdad and the Kurdistan regional government (KRG) claim jurisdiction.
"Our and Peshmerga are there to prevent the situation erupting because as soon as this command (Dijla) enters deep into the disputed areas... the area will ignite," said Azad Jendiani, spokesman for the political office of the Patriotic Union of Kurdistan which jointly rules the Kurdish region.
Iraqi sources said dozens of Iraqi armoured vehicles and tanks headed on Tuesday from a base in Taji, just north of Baghdad, to Tuz Khurmato, which lies in an area along the border demarcating the Kurdish region from the rest of the country.
"We have moved from Taji to Tuz Khurmato with orders to open fire immediately in response to any attack," said an intelligence officer attached to the troops.
Iraqi government officials did not immediately respond to calls seeking comment on the troop movements.
INTERNAL BORDER TENSIONS
Since the last American troops left the country in December, Iraq has been mired in political infighting among the Shi'ite, Sunni and Kurdish political blocks that constitute its fragile power-sharing central government.
Those tensions have been complicated further by growing friction between Baghdad and Kurdistan, which has run its own affairs since 1991, but is still dependent on the government for a share of the central budget.
Kurdistan and Baghdad disagree over who controls disputed land and the right to control oil in the Kurdish region. Deals signed by Kurdistan with oil majors like Exxon Mobil and Chevron have heightened the dispute.
The latest escalation began a few days ago when Iraqi troops tried to search the office of a Kurdish political party in Tuz Khurmato, triggering a clash with Peshmerga. One person was killed in the skirmish.
Kurdish troops were deployed to the area in response, armed with heavy weapons, machine guns and artillery, local police sources said.
Kurdish officials say the new Iraqi army command centre, known as the Dijla Operations Command, is a direct threat and a move to take control over oil-rich areas. But Prime Minister Nuri al-Maliki says the command centre is necessary to keep order in one of the most volatile parts of the country.
The Shi'ite leader has clashed increasingly with Kurdistan President Masoud Barzani, with the two sparring more aggressively since America's military withdrawal.
Washington intervened in August to help ease a standoff between Iraqi troops and Kurdish forces which came close to confrontation along their internal border in another disputed area near the Syrian frontier.