LONDON, Oct 18 (Reuters) - British Prime Minister Rishi Sunak will arrive in Israel on Thursday and meet with Prime Minister Benjamin Netanyahu and President Isaac Herzog, before travelling on to other regional capitals, his office said.

Sunak will share his condolences for the loss of life in Israel and Gaza as a result of the Oct. 7 attack on Israel by Gaza-based Palestinian Hamas gunmen, his office said, and warn against further escalation of conflict in the region.

"Every civilian death is a tragedy. And too many lives have been lost following Hamas’ horrific act of terror," Sunak said in a statement ahead of his visit.

He said a deadly blast at a Gaza hospital on Tuesday which killed hundreds of Palestinians should be "a watershed moment for leaders in the region and across the world to come together to avoid further dangerous escalation of conflict", pledging Britain would be at "the forefront of this effort".

Sunak will also urge the opening up of a route to allow humanitarian aid into Gaza as soon as possible, and to enable British nationals trapped in Gaza to leave.

At least seven British nationals have been killed and at least nine are missing since the attack on Israel, Sunak's spokesperson said earlier on Wednesday.

Alongside Sunak's visit, British Foreign Secretary James Cleverly, who visited Israel last week, will travel to Egypt, Turkey and Qatar over the next three days to discuss the conflict and seek a peaceful resolution, his office said.

Britain said the three countries were "vital to international efforts to uphold regional stability, free hostages and allow humanitarian access to Gaza".

Cleverly will meet with senior leaders there to discuss efforts to prevent the conflict spreading, the urgent need to open the Rafah crossing with Egypt to let aid reach those who need it and for Hamas to release hostages, Britain said.

Photo from AFP