By Sanjeeban Sarkar

June 27 (Reuters) - British oilfield services company Petrofac Ltd PFC.L on Tuesday said it expected an underlying net profit of $135 million to $145 million for the first half of 2017 as strong bidding activity in its core markets led to a robust order book.

Shares in the company were down 2.6 percent at 415 pence at 0810 GMT on the London Stock Exchange.

"High level of tendering activity is evidence of greater confidence in our core markets and we continue to have a very good pipeline of bidding opportunities," CEO Ayman Asfari said in a statement.

Bidding activity in the first half of the year was consistent with Petrofac's guidance of higher activity in its core Middle Eastern markets, CFO Alastair Cochran told Reuters.

Full-year underlying net profit would be weighted towards the second half of the year in a ratio of about 40:60 percent, he added.

Order book stood at $13 billion as of May 31, said the company, which builds and operates oil and gas facilities. It recorded an order book value of $14.3 billion in 2016 as orders picked up in its core Middle Eastern markets.

The company's high exposure to the Middle Eastern oil markets resulted in good backlog coverage for 2017 as record production in the region drove up contract awards.

Petrofac is under investigation by the UK's Serious Fraud Office (SFO) for its dealings with Monaco-based Unaoil, which Petrofac said it had engaged primarily in Kazakhstan to provide local consultancy services between 2002 and 2009.

Petrofac suspended its chief operating officer, Marwan Chedid, last month in response to the investigation, raising concerns among investors about the company's ability to win work.

CFO Cochran said on Tuesday the company was engaged with the SFO and had not paid any penalty, when asked if the company had set aside cash in case of a fine.

(Reporting by Sanjeeban Sarkar in Bengaluru; Editing by Gopakumar Warrier and Amrutha Gayathri) ((Sanjeeban.Sarkar@thomsonreuters.com; UK: +44 20 7542 1810; Outside UK: +91 80 6749 1136; Reuters Messaging: Sanjeeban.Sarkar.thomsonreuters.com@reuters.net))