Egypt stock markets extended their decline on Tuesday as foreign investors sold equities on fears of more protests after several of them broke out in Egyptian cities over the weekend.

Authorities rounded up more than 400 people in response to an outbreak of protests against President Abdel Fattah al-Sisi and security forces stepped up their presence in central Cairo, human rights monitors said on Monday. 

The blue-chip stock index plunged 4.2%, its lowest since January, with 26 out of 30 stocks on the index seeing a fall. The country's blue-chip index has lost 10.7% so far this week, leaving it with a meagre 1% gain so far this year.

The broader stock index EGX 100 declined 3%, the most since March 2017.

The country's biggest lender Commercial International Bank (COMI) fell 6.3%.

Exchange data showed foreign investors sold a net 776.8 million Egyptian pounds ($47.77 million) of stocks. COMI is a key holding for foreign institutions.

"Today, the selloff was again led by foreigners who were net sellers. They accounted for 27% of the total turnover," said Allen Sandeep, director research at Naeem Holding. "The selloff is coming amid far-fetched speculations that the protests would escalate."

Meanwhile, Saudi's index was up 1.5%, boosted by a 1.3% rise in Al Rajhi Bank 1120.SE , and a 2.8% gain in Riyad Bank.

On Monday, Saudi stocks joined the FTSE Russell index in their fourth of eventual five tranches and the S&P Dow Jones index in the second and final phase.

Petrochemical firms also gained after feedstock supplies from oil giant Saudi Aramco improved. Saudi Basic Industries 2010.SE was up 1.2%, while Rabigh Refining And Petrochemical 2380.SE jumped 4.1%.

In Dubai, the index closed 1.1% lower, pulled down by its top lender Emirates NBD Bank , which dropped 2.3%. Blue-chip developer Emaar Properties lost 1.2%.

A weakening property market in the United Arab Emirates is likely to put more pressure on the asset quality of the banking sector, Fitch Ratings agency said. 

Qatar's index traded 0.4% lower with Gulf's biggest lender Qatar National Bank shedding 0.9% and Qatar Insurance  down 3.2%.

The Abu Dhabi index traded flat with market heavyweight First Abu Dhabi Bank gaining 0.1%.

($1 = 16.2600 Egyptian pounds)

(Reporting by Ateeq Shariff and Shamsuddin Mohd in Bengaluru; additional reporting by Saeed Azhar in Dubai; editing by Uttaresh.V) ((AteeqUr.Shariff@thomsonreuters.com; +918067497129;))