Saudi Arabia's index declined 2.7 per cent on Monday afternoon, the biggest intraday decline since mid-October.
Al Rajhi Bank slipped 2.6 per cent and its top petrochemical maker Saudi Basic Industries fell 2.4 per cent.
"Regional geopolitical tensions and the US-China trade row are affecting market sentiment," said Nishit Lakhotia, head of research at Bahrain-based Sico. "Investors will take any opportunity to lock in profit after the recent gains, especially in Saudi Arabia."
Saudi Arabia said on Monday that two Saudi oil tankers were among vessels targeted by a "sabotage attack" off the coast of the UAE, condemning it as an attempt to undermine the security of global crude supplies.
Shares in National Shipping Company of Saudi Arabia (Bahri) dropped 3.3 per cent, after trading and shipping sources identified the Saudi vessels targeted as Bahri-owned very large crude carrier Amjad and crude tanker Al Marzoqah.
Bahri did not respond to a request for comment.
The Dubai index was down 2.9 per cent before slipping further to close at 3.9 per cent lower with the emirate's largest bank, Emirates NBD, closing down 3.6 per cent and the emirate's largest listed developer, Emaar Properties, sliding by 5.8 per cent.
Financials also pushed Abu Dhabi's index into the red, slipping to close at 3.3 per cent down. First Abu Dhabi Bank, the UAE's biggest bank, closed down 3.5 per cent, while Abu Dhabi Commercial Bank shed 4.6 per cent.
Waha Capital rebounded from earlier losses to close at 1.1 per cent up, a day after the investment firm reported a net loss of Dh57.8 million because of a revaluation of its investment in global aviation leasing firm Aercap.