The Foreign Office has urged “calm heads and de-escalation” after hundreds of pagers exploded simultaneously across Lebanon and in parts of Syria.
At least nine people were killed and thousands wounded on Tuesday in what appeared to be a sophisticated, remote attack.
An FCDO spokesperson said: “We continue to monitor the situation in Lebanon closely and the UK is working with diplomatic and humanitarian partners in the region. The civilian casualties following these explosions are deeply distressing.
“We urge calm heads and de-escalation at this critical time.”
Members of the militant group Hezbollah, the Iranian ambassador and thousands of other people were among the wounded.
A Hezbollah official speaking anonymously told the Associated Press that Israel had targeted the devices. The Israeli military declined to comment.
The Foreign Office also updated its travel advice to include information on the explosion of communication devices, saying British nationals in Lebanon should exercise caution and that hospitals may be very busy.
Foreign Secretary David Lammy urged Britons to leave Lebanon several weeks ago, saying that they risk “becoming trapped in a warzone” if they fail to do so.
Tensions have been rising between Lebanon and Israel, with clashes almost daily between the Lebanese militant group Hezbollah and Israeli forces since the war between Israel and Hezbollah ally Hamas in began in Gaza.
Hundreds in Lebanon and dozens in Israel have been killed in the clashes, which have also displaced tens of thousands on both sides of the border.
Israel said on Tuesday that stopping Hezbollah’s attacks in the north to allow residents to return to their homes is now an official goal.
Lufthansa suspended all flights to Tel Aviv and Tehran in response to the explosions.
The airline said all flights to and from those airports would be cancelled and routes would bypass Israeli and Iranian airspace up to and including September 19.