Saudi Arabia is on course to execute 150 people or more, for a second consecutive year, becoming one of the most frequent users of state executions to carry out judicial sentences, figures compiled by the human rights group Reprieve show.

The group also claims its figures show the kingdom is increasingly using secret courts to impose the death penalty on drug offenders, juveniles and political prisoners.

Many Gulf states use the death penalty and there is concern that executions are becoming the “new normal”. The Reprieve figures show 150 people have been executed this year, close to the 2015 high of 158, and way above the 2014 figure of 87.

Reprieve also suggested that although Saudi Arabia was the Gulf state most likely to use the death penalty, other states such as Kuwait were lowering the age at which the death penalty could be used.

Reprieve also finds that a large number of those killed were “state security” cases, involving people tried in secret courts – this includes political dissidents and people who were tortured into “confessions”.

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Many of those executed were arrested for drug offences, including quite a few foreign nationals, some of whom could well have been trafficking victims.

In January, Saudi Arabia executed 47 people in one day.

The numbers include juveniles – raising fears for those children who remain on death row, including Ali al-Nimr, Dawood al-Marhoon and Abdullah al-Zaher, who were arrested in relation to protests. Al-Mahroon was arrested aged 17 in 2002. Ali al-Nimr will turn 22 next week.

David Cameron, the former British prime minister, publicly called on the Saudi authorities to halt the planned executions of Ali, Dawood and Abdullah last year, and Reprieve understands that the UK foreign secretary, Boris Johnson, raised the cases with his Saudi counterpart as recently as September.

But Reprieve argues that the UK should be not just focusing on seeking assurances that the death sentences will not be carried out, but asking Saudi Arabia to commute the sentences and release the juveniles.

It claimed Dawood al-Marhoon was being seriously mistreated in a death-row prison, adding “we have had reports that he has been beaten and threatened with solitary confinement as payback after he complained about a previous instance of abuse. It has also emerged his health and that of other juveniles is suffering in prison. For example, the jail is reportedly ignoring a doctor’s advice on the food that should be given to juvenile prisoners.

More than two-thirds of all countries have now abolished the death penalty in law or practice. In the US, 18 states plus the District of Columbia have abolished it, and seven more have not carried out an execution for at least 10 years.

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Nevertheless, 2015 saw a large increase in the use of the death penalty worldwide. At least 1,634 people were executed, a rise of more than 50% from the previous year and the highest number Amnesty International has recorded since 1989. This total does not include China, where thousands more are likely to have been executed, but the relevant data is treated as a state secret.

The Reprieve research was published as the British foreign office minister Tobias Ellwood, along with the US secretary of state, John Kerry, met Saudi King Salman and crown prince Mohammed bin Nayef in Riyadh to discuss peace efforts in Yemen.

They were joined by leaders from Oman and the United Arab Emirates, and discussion focused on the humanitarian crisis in Yemen, as well as efforts to restart the UN-led peace process.

The Saudi foreign minister, Adel al-Jubeir, speaking at a joint news conference denied reports the US was scaling back its arms support to Saudi Arabia in protest at the conduct of its air campaign in Yemen.

Jubeir said: “This news that has been leaked contradicts reality. The reality is that converting regular bombs to smart bombs would be welcome because smart bombs are more accurate.” There were also reports that the US was scaling back its intelligence cooperation, but Kerry gave no hint of disapproval of the Saudis in his remarks.

The war in Yemen has also allowed extremist groups to flourish, as the local affiliate of the Islamic State group claimed responsibility for a suicide bombing on Sunday in the southern port city of Aden that killed at least 49 soldiers lined up to receive their pay.

Kerry’s visit to Saudi Arabia is probably his last before a new administration led by president-elect Donald Trump takes office.