BANGKOK - Thailand's air traffic communications body said on Wednesday it had back-up operations to ensure no disruption to air travel if hard-line anti-government protesters attempt to shut down its main control centre.

Protesters trying to topple the government are camped in central Bangkok and one faction has threatened to besiege the stock exchange and offices of the Aeronautical Radio of Thailand Ltd (AeroThai), part of the Ministry of Transport, which handles air traffic control communications.

AeroThai's offices in central Bangkok threatened by the protesters look after planes in air space beyond 50 miles (80 km) from Thai airports.

"AeroThai has prepared contingency plans to handle any situation that may affect our service ... For en-route services AeroThai has set up a back-up centre working parallel to our primary system," company president Prajak Sajjasophon told Reuters.

"We can assure you services will not be affected if protesters force our headquarters to shut down operations."

Flag carrier Thai Airways International also played down the potential for disruption.

"The airline has closely coordinated with AeroThai, which has prepared strict measures to cope with the impact from the protest for more than two months. We don't expect any problem with operations and the protesters should not be able to get access to the air traffic control tower,"  Executive Vice-President for Finance Wasukarn Visansawatdi told Reuters.

The main protest group in Bangkok is trying to stop ministries and other state bodies from functioning but it said on Tuesday the air traffic agency was not one of its targets.

However, one allied group, whose members include students and trade unionists, has threatened action against the agency and stock exchange if Prime Minister Yingluck Shinawatra does not resign by Wednesday.

A Reuters photographer said this group marched from its protest camp, but at midday (0500 GMT) members were at the attorney general's office, miles from the air traffic facility.

In 2008, in an earlier bout of political unrest, a group of protesters forced Bangkok's two main airports to close for more than a week.

Transport Minister Chadchart Sittipunt told reporters last week that U-Tapao military airbase in Pattaya to the south of the capital had been prepared as back-up if demonstrators targeted the Bangkok airports again.