Sexually transmitted infections are on the rise in Scotland, with reported cases of syphilis and gonorrhoea at their highest in decades.

New statistics from Health Protection Scotland (HPS) show diagnoses for several STIs rose between 2016 and 2017.

Experts say in the increase is concerning and the ongoing promotion of good sexual health is essential.

Genital chlamydia remained the most frequently diagnosed infection, with 15,685 cases reported in 2017.

The figure is up 4% from the previous year and the disease predominates in women and young people.

A 10% increase in gonorrhoea was reported, with 2610 recorded last year.

There has been a 64% increase in gonorrhoea diagnoses in the last five years.

HPS says the rise is largely down to transmission among men who have sex with other men.

The number of infectious syphilis diagnoses increased from 356 in 2016 to 397 in 2017. It is the highest annual total in nearly 70 years.

There has been a threefold increase of the STI among men who have sex with other men over the last few years.

Most men who were diagnosed with an STI had met their partners via the internet or dating apps, HPS found.

The HPS report said: "In Scotland, infectious syphilis remains a serious public health problem, particularly among men who have sex with other men (MSM)

"The increase in diagnoses, observed in 2017, underlines the importance of a concerted public health response.

"There is evidence of high-risk behaviour among a proportion of MSM in Scotland through various behavioural studies."

A recent study found more than half of 1500 men who have sex with other men in Scotland had intercourse without a condom in the least year.

Lesley Wallace, epidemiologist at HPS, said: "Diagnoses of several acute sexually transmitted infections continue to increase in 2017, continuing the trend in the past few years.

"The emerging pattern is one which indicates relatively stable levels among heterosexual men and women, notably for gonorrhoea and syphilis which remain relatively uncommon, and for chlamydia which is much more common, especially among young people.

"The main concern is the high level of gonorrhoea, and the increase in chlamydia and infectious syphilis, in men who have sex with men (MSM).

"These data indicate a continuing high level of casual unprotected sexual intercourse among an appreciable minority of MSM.

"Work is currently being done to explain why this is happening.

"The ongoing promotion of good sexual health is essential with one of the key goals being the prevention of infection; this includes advice on condom use for casual sexual intercourse and accessing healthcare services for STI testing if at risk."