AUSTIN, Texas (Reuters) - Texas' attorney general warned Secretary of State Hillary Clinton on Thursday that international election monitors planning to observe balloting in the state were not above Texas law.

Republican Attorney General Greg Abbott's letter to Clinton was the latest move in his campaign to ensure that the Vienna-based human rights watchdog Organization for Security and Cooperation in Europe did not mess with Texas.

"It appears that OSCE is under the misimpression that the State Department can somehow help its representatives circumvent the Texas Election Code," Abbott wrote. "Texas law prohibits unauthorized persons from entering a polling place â?? or loitering within 100 feet of a polling place's entrance â?? on Election Day. OSCE monitors are expected to follow that law like everyone else."

In a letter on Tuesday to the Warsaw-based Office for Democratic Institutions and Human Rights, the OSCE's monitoring arm, Abbott had warned that failure to follow Texas law could subject OSCE representatives to criminal prosecution.

Janez Lenarcic, director of the monitoring arm, told Clinton on Wednesday about its "grave concern" with Abbott's letter, saying the threat of criminal sanctions was unacceptable and unprecedented.

The 56-member OSCE routinely sends monitors to elections. For the November 6 U.S. elections, it has a core team of 13 experts from 10 OSCE countries based in Washington and 44 long-term observers deployed across the country, it said.

State Department spokeswoman Victoria Nuland noted that the OSCE had sent observers to U.S. general elections since 2002.

The OSCE has assured Clinton and Texas authorities that OSCE observers are committed to following all U.S. laws, Nuland said.

"To my knowledge it's the only state that came forward and said, 'Please reassure us, that you're gonna follow our state electoral law.' And they have now been reassured," Nuland told a news briefing in reference to Texas.

But in his letter to Clinton, Abbott took issue with Lenarcic's assertion to the secretary of state that Abbott's threat of criminal sanctions contradicted commitments made by the United States, including in the 1990 OSCE Copenhagen document.

"The fact that representatives of the United States joined the U.S.S.R, Yugoslavia, Romania, and other OSCE member-nations in signing a document at a 1989 conference in Copenhagen has absolutely no bearing on the administration of elections or laws governing elections in the State of Texas," Abbott wrote.

He added that the OSCE was not above the law.

Abbott told Reuters on Wednesday he was considering legal action against OSCE if it did not concede that it would follow the state's laws.

(Reporting By Corrie MacLaggan; Additional reporting by Andrew Quinn; Editing by Peter Cooney)