April 11 (Reuters) - Russia on Thursday advised against

travel to the Middle East and German airline Lufthansa extended

a suspension of its flights to Tehran, as the region was kept on

edge by Iran's threat to retaliate against Israel for an attack

in Syria.

Iran has vowed revenge for the April 1 airstrike on its

embassy compound in Damascus which killed a top Iranian general

and six other Iranian military officers, further escalating

tensions in a region already convulsed by the Gaza war.

Russia's foreign ministry told citizens they should refrain

from travelling to the Middle East, especially to Israel,

Lebanon and the Palestinian territories.

"We strongly recommend that Russian citizens refrain from

traveling to the region, especially to Israel, Lebanon and the

Palestinian territories, except in cases of extreme necessity,"

it said.

"The tense situation in the Middle East region persists,"

said the foreign ministry, which first issued such travel advice

in October when it urged Russians not to visit Israel and the

Palestinian territories after Hamas attacked Israel.

Conflict has spread across the region since the eruption of

the Gaza war, with Iran-backed groups declaring support for the

Palestinians waging attacks from Lebanon, Yemen and Iraq. Tehran

has avoided any direct confrontation itself with Israel or the

United States, whilst declaring support for its allies.

Israel has not declared its responsibility for the April 1

attack, for which Iranian Supreme Leader Ayatollah Ali Khamenei

said on Wednesday Israel "must be punished and it shall be",

saying it was tantamount to an attack on Iranian soil.

U.S. President Joe Biden said on Wednesday Iran was

"threatening to launch a significant attack in Israel".

Biden said he'd told Israeli Prime Minister Benjamin

Netanyahu, "our commitment to Israel security against these

threats from Iran and its proxies is iron clad. Let me say it

again, iron clad - all we can to protect Israel's security."

Oil prices ticked up during trade on Thursday, after rising

a dollar a barrel in the prior session, as investors braced for

a worsening of the Middle East crisis, potentially involving

Iran, the third-largest oil producer in OPEC.

Late on Wednesday, an Iranian news agency published an

Arabic report on social media platform X saying all airspace

over Tehran had been closed for military drills. The agency then

removed the report and denied it had issued such news.

In an apparent response to Khamenei, Israeli Foreign

Minister Israel Katz said on Wednesday that Israel will respond

if Iran attacks Israel from its own soil.

LUFTHANSA EXTENDS SUSPENSION

Lufthansa said on Wednesday it had suspended flights to

Tehran due to the situation in the Middle East. On Thursday, the

airline said this had been extended until probably April 13.

A spokesperson said Lufthansa had decided not to operate a

flight from Frankfurt to Tehran last weekend to avoid the crew

having to disembark to spend the night in Tehran.

Lufthansa and its subsidiary Austrian Airlines are the only

two Western carriers flying into Tehran, which is mostly served

by Turkish and Middle Eastern airlines.

Austrian Airlines, which is owned by Lufthansa and flies

from Vienna to Tehran six times a week, said it was still

planning to fly on Thursday but was adjusting timings to avoid

an overnight layover.

There was no immediate word from other international

airlines that fly to Tehran. Iranian air space is also a key

overflight route for Emirates' and Qatar Airways' flights to

North America.

(Reporting by Ilona Wissenbach in Frankfurt; Shariq Khan in New

York; Emily Chow in Singapore; Writing by Tom Perry; Editing by

Ros Russell)