ISTANBUL (Reuters) - Turkey’s lira slid to its lowest level against the dollar in more than a month on Monday over concerns about Ankara’s planned incursion in northern Syria and a warning from President Donald Trump that he could “obliterate” the Turkish economy.

A merchant counts Turkish lira banknotes at the Grand Bazaar in Istanbul, Turkey, March 29, 2019. REUTERS/Murad Sezer

Investors have been monitoring tensions between Ankara and Washington in recent months, with the NATO allies at odds over a range of issues including policy differences in Syria and Turkey’s purchase of Russian missile defence systems.

Turkey has repeatedly threatened to carry out an incursion against the U.S.-backed Kurdish YPG militia in northeast Syria, accusing the United States of stalling efforts to establish a “safe zone” there along the Turkish border.

Following a phone call between Trump and Turkish President Tayyip Erdogan, the White House said on Sunday U.S. forces would not support a Turkish incursion and would leave the area.

On Monday, Trump threatened to “totally destroy and obliterate” the Turkish economy if Turkey took any action he considered “off-limits”.

The lira TRYTOM=D3 declined more than 2%, trading at 5.8305 at 1830 GMT, after closing at 5.7000 on Friday. Earlier, it slipped as far as 5.8375, its weakest level since Sept. 2.

“While the statement from the United States gives a green light to the military operation in Syria that Turkey has mentioned for a long time, it leaves many question marks regarding how the process will develop,” said a forex trader who did not want to be named.

Turkey's dollar bonds also fell, with the 2038 issue US900123CB40=TE down 1.3 cents.

Turkey’s lira lost nearly 30% against the dollar last year over concerns about political interference with monetary policy, as well as a deterioration in relations between Washington and Ankara. It is down about 8% this year.

Turkey's BIST100 main share index .XU100 closed down 0.45%, while the banking index .XBANK declined 1.72%.