A deal for an estimated $2.1bn-worth of small warships is expected to underpin the three-day visit of King Felipe VI of Spain to Riyadh, which began on 14 January.

Spanish shipbuilding company Navantia said advanced negotiations are ongoing to build five warships for the Saudi navy, according to French news agency AFP citing an unnamed Navantia spokesman.

The transaction is understood to involve five Avante corvettes, which are designed primarily for offshore patrolling.

Several international human rights groups have opposed the potential sale, describing it illegal if they were to be used in the ongoing war in Yemen.

“Any possible arms sales to Saudi Arabia that could be used in Yemen is illegal because it violates Spanish law and international arms trade,” Esteban Beltran, director of Amnesty International in Spain, said in a statement.

Saudi Arabia leads a multi-county Arab coalition that launched a military offensive in Yemen in March 2015. The coalition aims to restore the legitimate government led by President Abdrabbu Mansour al-Hadi and hold back the Houthi fighters, believed to be backed by Iran, from advancing in major parts of the country.

The coalition’s air strikes are responsible for the majority (60 per cent) of the close to 4,000 civilian casualties in the 21-month civil war, the United Nations’ human rights office said in 2016.

Rising pressures from rights groups and the UN have forced the US government in December 2016 to announce it is cutting back on the sale of weapons, specifically precision-guided weapons, to Saudi Arabia.

However, the sale of $1.15bn-worth of tanks and other land-based weapons to Saud Arabia, approved by the US Senate in September 2016, is understood to still go ahead.

In June 2016, Qatar’s Defence Ministry signed a $4bn contract with Italy’s Fincantieri to build seven surface vessels for the Qatar Emiri Naval Forces, including four corvettes.

Corvettes are a smaller version of frigates, considered a vital component of a country’s naval defence fleet.