Turkey's benchmark stock index fell 1.18 percent to close at 108,451.70 points on Friday with a 6.1 billion Turkish lira ($1.78 billion) trade volume.
Borsa Istanbul's BIST 100 index declined 1,291.25 points, from 109,742.95 points at closing on Thursday, while the banking and holding sector indices were up 1.92 and 0.97 percent, respectively.
On the last trading day of the week, the BIST electricity index advanced the most with a 1.23 percent increase and the BIST mining index was the worst performer, falling 2.92 percent.
Stocks of energy and mining company Park Elektrik (PRKME) were the top gainer of the day -- with a 8.37 percent rise -- while shares of poultry and feed producer Banvit went down 6.87 percent, the biggest drop on Friday.
The BIST 100's most traded stocks were state lender Halkbank (HALKB), national flag carrier Turkish Airlines (THYAO), private lender Garanti (GARAN), followed by mining and energy company Ipek Dogal Enerji (IPEKE) and pharmaceutical company Eczacibasi Ilac (ECILC).
Borsa Istanbul's Gold Exchange index rose 0.96 percent, while the price of gold per kilogram stood at 148,300 Turkish liras (around $43,405) as of 4.30 p.m. local time (1330GMT) on Friday.
On a weekly basis, the benchmark index went down 1.41 percent closing at 110,010.49 points on Thursday Aug. 31, which was the last trading day of the week due to a four-and-a-half-day break for the Muslim holiday of Eid Al-Adha.
Last month, the index climbed from closing at 107,531.44 points on Monday, July 31 -- marking a 2.30 percent monthly increase.
Since the beginning of this year, the BIST 100 has risen nearly 40 percent and hit its highest peak at 110,530.75 points during trading hours on Monday, Aug. 28.
- USD/TRY exchange rate
The Turkish lira continued to gain ground against the U.S. dollar on Friday. The dollar/lira exchange rate dropped to 3.4080 by 5 p.m. local time (1400GMT), compared with 3.4130 at Thursday's close.
The exchange rate decreased by nearly 1.6 percent on a weekly basis, compared to 3.4630 on Thursday, Aug. 31.
One dollar was exchanged for 3.51 on average last month, while the first eight months' average USD/TRY rate was 3.61.
The USD/TRY rate saw sharp fluctuations after last year's July 15 defeated coup and climbed to its historic hike -- around 3.94 liras -- in mid-January this year.
According to Turkish Central Bank data, the dollar/lira rate was 3.02 on average last year and 2.71 on average in 2015.