Activity in Russia's manufacturing sector grew at the slowest rate in three months in April, a business survey showed on Thursday, as expansions in output and new orders softened slightly from previous highs.

The S&P Global Purchasing Managers' Index (PMI) for Russian manufacturing fell to 54.3 in April from an 18-year high of 55.7 in March, staying above the 50 marks that separates expansion from contraction.

Russia has been spending heavily on the manufacturing of military equipment and weapons since it invaded Ukraine in February 2022, buoying a sector that otherwise may have suffered as some markets shunned Moscow.

Production in April grew at the second-fastest rate in seven years, while Russian firms noted a steep expansion in new sales to domestic customers.

"Although the slowest for three months, the rate of growth was historically robust as firms highlighted new client wins and successful marketing campaigns", S&P Global said in a statement.

The strong growth in new orders led to firms to expand their workforces for the third successive month. Despite the boost in workers, firms struggled with backlogs, and output prices rose as delivery delays continued to plague businesses.

"Respondents often mentioned higher transportation and raw material prices", S&P Global said.

Despite those challenges, firms remained upbeat in their expectations for future output.

"Hopes for greater production in the coming 12 months were reportedly underpinned by the development of new product ranges and hopes of stronger customer demand", S&P Global said. (Writing by Lucy Papachristou; Editing by Toby Chopra)